The idea of a Light Type is always something that, while I admittedly can't easily explain it, always annoyed the fuck out of me. Whenever someone brought it up it always sounded just such a really bad fan idea that wasn't thought through well at all. It's most often theorized as a counterpart to Dark; which is bad to me because 1. Dark sort of... already does have a counterpart in Psychic in a weird way, and 2. That makes the type incredibly one-dimensional and boring if that's all you're introducing it for. It also just reeks of the all-too-common "dark vs light; evil vs good" trope in Anime and RPGs which I am so glad Pokémon has managed to avoid.
By contrast; and this probably deserves it's own thing, but I much much much prefer the Fairy type. It doesn't try to be a Dark counterpart and hence finds it's own identity; and while it might seem arbitrary due to how specific 'fairy' is compared to concepts like rocks and water, I see it like Bug, Ghost and Dragon where it caters to a specific sub-species which can be wide and varied. I also don't know where people are coming from when they say the type matchups were handled badly - aside from being resistant to Bug (which is, admittedly, really dumb when Bug has enough problems and it doesn't even make sense thematically) I do find it handled very well. Let's start off with the three things it's super effective against and resists - Dragon, Fighting and Dark. Those were needed. Dragon and Fighting spam, if you played Gen 4/5, were fucking everywhere due to the insane buffs they received in those two gens. Now that leaves Dark, which wasn't overpowered at all though mostly due to the fact that it didn't have high base power moves. Enter Gen 6, which gives it fucking Knock Off and the removal of Steel's resistance to it. At that point, were it not for Fairy I'd argue a lot of Dark-types like Bisharp would become really broken. If you've played the OU meta recently or even near the start of XY you'll know the Dark Spam is real; heck in the No Mega ladder Knock Off dominates the entire thing. Meanwhile, the things that are super effective against it are Poison and Steel, neither of which were previously good attacking types and people complain you have to run them. Well, good I say! It's great to see some variety in attacking moves and I think that's partly what the Fairy type set out to do and succeeded. Heck if you take a look the types themselves offensively aren't really that bad - they have some pretty neat moves too - they were just outclassed and not worth using aside from a few Pokémon's STABs. Steel has recently become a popular offensive type in OU and is great regardless of Fairies; it's not like you're running something unviable just to hammer them. And hey, I fucking love Mega Beedrill so any excuse to make it better is good with me. Finally Fire resisting it... eh, that's cool, a typing this good did need that extra resist, especially with a type that isn't that bad defensively and is relatively common.
And to make a final point on the fairies; I will say that aside from a few obvious outliers - but come on guys, did you really expect fucking Mega Diancie to not be conceptualized as OP? - while you would expect a typing this good to be broken, it's balanced out by the fact that the Pokémon that do get it have low stats. Aside from Sylveon and Azumarill, the only real hard-hitting fairies are either Legendaries or Megas, and really those two groups are supposed to be stupidly powerful anyway. Clefable has low stats, Mawile has low stats, Klefki has low stats; even Fairies with relatively high stats like Granbull, Florges and (non-mega) Gardevoir have big problems in either defensive stats or speed.
So really, at the end of the day, I never really got the big negative reaction to the Fairy Type. Aside from the dumb resisting bug thing; it's well-balanced, well made, it brings a lot of unique and balancing traits to the game, and it has a much bigger identity than a fucking Light type would. Seriously what would light type even be gadyuigrjk
Light-Type Failing: I think the thing that bothers me about Light-type is that it shows a lack of understanding of what the Dark-type is. They want a Light-type because the opposite of light is dark. Fair enough thinking... except that's not what the Dark-type is. This all stems to the Japanese name for the type: Evil-type. The Dark-type doesn't represent darkness or the night (some do, though those are the exceptions and even then they still have traits that I'm about to mention) but rather represents foulness, trickery, thievery, and overall dirty fighting. Dark-types do whatever it'll take to win, pulling out every trick in the book to do so. They'll bite, put in a false sense of security, attack you when you least suspect it, and even call upon darker powers. We can define what a Dark-type Pokemon is and how'll it act.
So, the question is what would a Light-type be? Will they be heroic or good nature? Well, and call my a optimist, most conscious beings try to do what's best for them and those around them. No one sees themselves as villains, its only people with a deviant behavior who see themselves as villains and go out to do bad things. Basically being good IS the norm, it doesn't need its own type to show that a being would do the right thing if presented with it. Well what about a Pokemon being made of light/energy? Well aside from it stopping it being the opposite of what the Dark-type is, that's kind of vague characteristic and pretty one note. So tell me, what would this theoretically Light-type be?
As the final nail in the coffin, Fighting-type is essentially the opposite of the Dark-type. Fighting-types are Pokemon who practice a certain form of martial art or other fighting technique. Usually practitioners of these fighting styles are disciplined and they fight with a set of rules. Where a Dark-type does what it takes to win and thus have no organization, a Fighting-type will not go against its own morals giving it a strong sense of focus. Fighting-types beat Dark-types because they refuse to fall for the Dark-type tricks and remain focus on their fighting style while the Dark-type struggles to figure out what to do now that none of it tricks are working. And since it was brought up, I see Psychic types are sort of intellectuals who rely on their opponent's thinking and behavior being normal so they can easily predict what they'll do. Fighting-types are weak to Psychic-type because the Psychic-type perfectly knows what the Fighting-type will do, there's no secrets. But Dark-types are random and think on the spot, how can a Psychic-type even prepare for that? Answer: They can't, which is why Dark is immune to Psychic. Alternatively another explanation is that the Dark-type's thoughts are so foul that a Psychic-type doesn't want to read it leaving them exposed.
Fairy-Type Succeeding: On the other hand, Fairy-types have an definable identity. Multiple religions and mythologies talk about fairy-like creatures of all sorts and in detail. We have fairies which are good, evil, helpful, pranksters, curious, mysterious, ethereal, and many things else. But what they all have is that their magical on some level. They're like Dragons and Ghost type in that way. Actually I've always split Pokemon types into 3 categories:
Element: Ground, Rock, Steel, Fire, Water, Grass, Electric, Ice
Trait: Normal, Fighting, Flying, Poison, Psychic, Dark
Creature: Bug, Ghost, Dragon, Fairy
While I'm sure you can argue about some placements, I think the categories themselves are self-explanatory and makes sense.
Fairy Matches: It being strong against Dragon, Dark, & Fighting and weak to Poison & Steel doesn't bother me at all, I'm just a bit confused about some other small things.
Bug resistance. While I get it on one level, fairy creatures I often presented with bug traits, the problem is not all fairy creatures are like that. If anything I kind of expected them to have some relation to Grass-types (though not like they needed something that resisted them either) being fairies are often depicted as being natural creatures. Sure not all faeries are, but I think more are presented being being a form of nature then having bug traits.
Resisted by fire. While I always approve of Fire-types getting a buff, I don't really see the relation here. Some have come up with loose explanations like forest fires would temporarily destroy homes of fairies and in some RPGs a flash of fire can blind a fairy, but those feel like long stretches.
Neutral to Normal and Ghost. Really? Like the reason I imagine the Fighting-type not being good against a Fairy would also make a Normal-type not good against a Fairy. Infact most often fairies if folklore LOVE to mess with normal people. And Ghost-types are just as ethereal as a Fairy is, you'd think there maybe some relation (then again I suppose they both can cancel each other out?).
However what its super effective against and weak too are the most important things to get right. People complain Fairy is OP because they now are being forced to change up their strategies. Guess, what, THAT WAS THE POINT! That's ALWAYS the point of introducing a new type! Dark and Steel was introduced because Psychic was OP in Gen I (among other reasons, but that's a main one). And after a few years and more and more Pokemon and Moves were introduced it was noticed Dragon- and Fighting-types were becoming OP (and Dark-type becoming a very handy utility type). At the same time they noticed Poison and Steel being given very limited roles, Poison mainly existed as Toxic while Steel was just used as a wall. So they came up with a type that nerfed the OP types and buffed the types that have been mitigated roles.
Now when they first introduced Fairy-types I can admit I wasn't sure how to feel (I know I'm judging a book by its cover, but did they really need to use so much pink?), but now having it be around for a while I can say its proven itself as a type. It has problems, but what type doesn't? I also expect next Gen to maybe see it get a small nerf or other types getting a small buff, at least in Move Power. And while I did see some criticism toward the Fairy type, I mostly ignore them as I was much more entertained by another thing that came about the introduction of Fairy-types: