I fundamentally disagree with this, and I'll start off by saying if this is your stance then it's gonna be particularly hard to convince you otherwise because we have inherently different beliefs on what we want out of an LC metagame. Diglett is not like pursuit trapping. Pursuit doesn't automatically prevent you from switching and, unless you're a Gastly or Abra, allows you to make a proper play or not. This makes Diglett massively better than pursuit and probs shouldn't be brought up in comparison. I also don't believe in making entire groups of Pokémon virtually unusable, which btw is different than metagame trends making certain pokemon less viable in a particular metagame. Diglett, which floats around the 40-50% usage tier in tournaments, will trap the mons in question consistently, so what's the point in running them? I don't see this as healthy metagame formation but rather forceful exclusion.There's two main things that Diglett provides that I feel are good for LC. Diglett provides a consistent way to guarantee removal of dangerous Pokemon who are otherwise difficult to actually KO - think Pursuit Trapping but better. Diglett also helps keep some Pokemon not just down but nearly non-existent which I'd also say is definitely desirable in LC. I'll start with why I believe the first is important, then move to the second.
Again, I'm pretty far on the other spectrum on this. Even that initial statement, "guaranteed kos", I don't think should sit well with competitive pokemon players in general. That's the point of playing this game, nothing's guaranteed and you should have to work for ko's. That's part of what makes playing this game fun and interesting. I don't think guaranteed ko's are healthy at all, and this is why I think trapping in general comes up as often as it does. Next, you reference bulky LC mons that never die thing. You're right about the BW thing, except the problem is that the bulky wall trope hasn't existed since BW. The knock off buff completely eviscerated any notion that defensive mons outweigh offensive, and I've only seen that idea get substantiated more with the advent of z-moves. Defensive mons, maybe aside from Foongus, struggle to keep up in LC, and I think knock off and overall offensive pressure have more to do with that than Diglett. Heck, the really strong defensive mons like Spritzee are not what Diglett is trapping, although it can in a pinch possibly, but rather dangerous offensive threats and defensive checks to threatening mons.First, guaranteed KOs. Diglett provides strong, tangible counterplay to the "bulky Pokemon that sticks around forever" trope that's existed ever since BW and Eviolite dropped. This is Pokemon like Mienfoo, Foongus, even Pawniard and Spritzee to an extent. For Mienfoo and Foongus a lot of points as to why Regenerator isn't exactly the most balanced thing ever were brought up (although Regenerator shouldn't be banned either), and Diglett's presence forces Mienfoo and Foongus to play more conservatively after they've been weakened, rather than being able to continuously wear down the opponent while not suffering similarly.
Again, I don't think these mons exist in the current meta, but while you argue it's because of Diglett, I argue it's for reason such as Knock Off and threats like clamperl vullaby mudbray 2hkoing or ohkoing everything in sight. This is not BW, which btw is still as offensive as ever in its current LCPL state.Responses to this might include examples of other metagames, where bulky Pokemon who stick around for a long time are prevalent in stall and how that, while subjectively 'unfun', isn't unhealthy. The different lies in the fact that the bulky LC Pokemon in question are nowhere near as passive as stallmons usually are - Mienfoo, Foongus, and Spritzee are all rather powerful and can actively win games as opposed to the "not losing" that stall attempts to do. Diglett allows playstyles like HO to overcome balance or bulky offense, rather than having to fight and be taken out by a Pokemon that refuses to die.
I never once argued that I think LC is too samey and I don't like using the same pokemon over and over again. I argued that rather than shape the metagame in a healthy manner, Diglett completely eliminates the ability to use certain pokemon like no other mon does. You don't have counter play and you have no guarantee that you can use those pokemon consistently and to the best of their ability. I have no problem finding new pokemon to use, I simply have a problem with a single mon legitimately telling me "nope" and laughing in my face.The second one is related to reducing diversity. While people might complain that LC looks very samey, that there's no room for experimentation, or that there's no reason to use lesser seen Pokemon, I definitely disagree with that and encourage you to actually try and break the mold yourself before giving up. We've seen Clamperl be rediscovered and rise to prominence, Tirtouga not be considered just "Onix/Kabuto but better vs Torchic", and even Drowzee used successfully. Having a Pokemon work to moderate levels of success is not a particularly high bar to achieve, even in LC's current state.
I am scared of none of those pokemon you mentioned if I don't have access to Diglett and my team building processes would probably be unaffected. Cyndaquil, Binacle, Skrelp, and Blitzle, really? Nevertheless, despite the fact that Ponyta will be better, counter play exists and the metagame will adapt. There is no counterplay to Diglett, you are trapped.LC has over 250 legal Pokemon. While more than a quarter of those Pokemon are directly outclassed in every way or are unusable (things like Weedle or Fomantis), many more fill the spot of "usable with some team support". Pokemon like Cyndaquil, Binacle, Skrelp, Blitzle, all of them can be used, they just aren't as good generally speaking. However, Diglett keeps many of them in check hard enough that they won't be used, making the teambuilding burden of checking them significantly lessened. There's a claim that Diglett puts a heavy burden on teambuilding - imagine how much more you'd have to stretch to account for Z-move Skrelp, bulky 2 move coverage Ponyta and Larvesta, NP 3 attack salandit, recycle Magnemite being used even more, bulky chou, voltturn being absolutely everywhere, ect ect. Diglett means you can't easily use some Pokemon, yes, but it also means there's a low risk that you'll have to fight them. And there's a lot more potential threats than there are slots to cover them all.
I don't really see this as evidence as, like you said, this was a completely different gen, Dig didn't have access to z-eq and again I don't ever remember seeing ORAS in a state of bulky mon domination other than maybe Porygon but lucky for us that shit's banned lol.On a more personal level, I also speak from the time we did a suspect test and banned Diglett from the ladder. While this was in another gen and things could certainly have changed since then, I have not so fond memories of that incredibly shitty metagame where fat things didn't die for ages, burns were spread freely, and if you went two games without encountering half a team of voltturn mons you were lucky.