So obviously I missed some stuff, and this will all be discussed. But while I may not think that mega's were a worse addition, I do think that they were a lazier addition. Dynamax simply has more features and new things to go with it, while still being original.
First, why is the first half your post invisible?
Second, yYeah, Dyna/Gigantmax sound better than Mega when you short sell it like that & don't include any of the cons. Think a better comparison list is this:
MEGA EVOLUTION:
The Numbers:
# 46 Pokemon get Megas; of which 2 get two Megas for a total of 48. Number increases to 50 if you count Primal Reversion as a kind of Mega Evolution.
# Generation Breakdown: 13 RBY, 6 GSC, 20 RSE, 5 DPPt, 1 BW, 1 XY
Pros:
+ Each gets a unique design meant to be an exaggeration/enhancement/ascension form of that Pokemon.
+ Each gets an additional 100 BST to their stats which are individually applied to best fit that Mega Pokemon's needs; in addition to this some Pokemon "lesser" stats were further decreased and allocated to other stats giving a further boost.
+ Some got new Types & Abilities that, combined with the stat increases, helped either strengthen what the Pokemon was already good at or gave them a new niche.
+ Were given to an even mixture of already strong/popular & to average/weak/unpopular Pokemon; many in the later category became competitively viable in higher tiers like OU & Ubers.
+ Once Mega Evolved the Pokemon stayed Mega Evolved even when switched out.
+ Can be used anytime in any battle; this means in-game doesn't affect the flow of the story.
Cons:
- Only a handful of Pokemon got a Mega & the concept is limited to fully evolved Pokemon.
- For some Mega Pokemon the +100 BST wasn't enough of a boost; in addition some stat increase decisions did not help the Mega Pokemon (such as increasing the inferior offense stat, making it feel like a dump stat to not make the Mega too powerful).
- Sometimes the way a Mega Pokemon's stats were redistributed changed how they played meaning you couldn't use their regular form a bit & then Mega Evolve and continue playing the same way (or at least do so in a way that makes the most use of it).
- Mega Pokemon that gain new Types sometime struggle to have a good STAB move to use with it; infact some of the new Abilities were purposely made to remedy this problem which some may argue wasted the Ability slot.
- Some Mega Pokemon Abilities weren't as good as one of their normal Abilities.
- For a Pokemon to Mega Evolve they needed to hold their Mega Stone; some would argue wasting the Item slot. And since only one Pokemon can Mega Evolve, if you wanted to be flexible which Pokemon to Mega Evolve you'd have to waste the Item slot on each Pokemon.
- Since many strong/popular Pokemon got a Mega, and you could only Mega Evolve once per battle, that meant a good number of the time they were used over the other average/weak/unpopular Pokemon.
Z-MOVES:
The Numbers:
# 18 Z-Moves for each Type; 17 unique Signature Z-Moves (some shared with other Pokemon); 35 total.
# Generation Breakdown For Signature Z-Moves: 6 RBY, 11 SM
Pros:
+ Any Pokemon can use the normal Z-Moves; only limitation is the Type of moves the Pokemon can learn.
+ Z-Moves turn even the lowest Power move into a hard hitting attack; Z-Move's Category is based on the base Move's Category.
+ Status Moves have an additional beneficial effect when powered by a Z-Move.
+ Signature Z-Moves tend to make the changed Move more powerful than it would have with a normal Z-Move.
+ Signature Z-Moves come with their own unique animations with the Pokemon Model (swapping in a different distorts the swapped Pokemon into fitting the skeleton of the intended model).
+ Signature Z-Moves sometime comes with a secondary effect (normal Z-Moves do not; though all Z-Moves do deal 25% damage if the user used a Protect variant).
+ Can be used anytime in any battle; this means in-game doesn't affect the flow of the story.
Cons:
- Because Z-Moves go off a base Move, what Z-Move a Pokemon can use can vary between different Pokemon (and then there's the question of what the base Move in question is, notably it's Power & Category).
- Z-Moves are one-use. Though they hit strong or give Status Moves a beneficial effect, if you had to go out of your way to get a a base Move to do a certain Z-Move that's not so useful outside access to that Z-Move, you're stuck with that Move potentially using up one of your four Move slots.
- Since a Pokemon needs to hold a Z-Crystal to use a Z-Move, not only does this use up their Item slot (and if a Z-Move is used up it essentially leaves the Pokemon without a Held Item; this compared to Mega Pokemon where the Held Item was given up for permanent boosts) but they can only use the Z-Move of that Type; Also, since Z-Moves are once per battle, if you want flexibility which Pokemon can use a Z-Move you'll have to use their Item slot (another small branch to that, while in-game you can give Pokemon the same kind of Z-Crystal, PvP Item Clause forces all Z-Crystals to be different Types).
- What Pokemon got Signature Z-Moves was limited to Gen I & VII.
- Signature Z-Moves require a specific Move which could limit a Pokemon's Moveset, especially if the base Move isn't a desired Move.
DYNAMAX/GIGANTAMAX:
The Numbers:
# 33 Gigantamax
# Generation Breakdown For Gigantamax: 12 RBY, 1 BW, 19 SwSh, & Melmetal
Pros:
+ Any Pokemon can Dynamax.
+ Increases HP, at max level doubles it. Damage calculation is kept the same. When Dynamax/Gigantamax ends the amount of HP the Pokemon has left is based on percentage.
+ Changes all offensive Moves into harder hitting Max Moves of the same Category of the base Move and has a (usually) beneficial secondary effect: Raising user & allies stats, decreasing opponent's stats, summing Weather, or summoning Terrain. All Max Moves & G-Max Moves also deal 25% damage if the user used a Protect variant. Meanwhile all Status Moves turn into Max Guard which protects from all damage even from Max Moves & G-Max Moves.
+ Can hold any Item and, depending on the Item, usually benefits from its effect.
+ Gigantamax get a unique design meant to make that Pokemon look like a giant kaiju or natural/manmade structure.
+ Gigantamax get unique G-Max Moves that, in addition doing more damage than normal Max Moves, come with their own unique effect. There are also no specific Move requirement, depending the G-Max Move's Type it replaces the Max Move of that Type.
Cons:
- Only lasts 3 turns. Arguably this is better for competitive, though you can still only Dynamax/Gigantamax one Pokemon per battle.
- Because HP is the only stat affected and all Moves are changed either into a Max Move/G-Max Move or Max Guard, while any Pokemon can Dynamax not all Pokemon may be able to use it's time as effectively as others.
- Because all Status Moves change into Max Guard must plan ahead of time when to use Status Moves before or after Dynamax/Gigantamax.
- Because of the size changing mechanic and changing all Moves into Max Moves or G-Max Moves, certain Abilities & Held Items have no effect while Dynamaxed/Gigantamaxed.
- Max Moves, notably the stat changing ones, may not have the effect you want for that Type. Have to choose either the Type or the effect, if that Pokemon has access to the Max Move with the desired effect.
- Because the G-Max Move replaces the Max Move of the Type it shares, you have to pick either the G-Max Move Effect or the Max Move effect.
- There is really no difference between a Dynamax and Gigantamax aside from the unique G-Max Move.
- Can only be used in places with a Power Spot; this means in-game it affects the story where battles take place if they want the opponent to be able to Dynamax/Gigantamax.
- What Pokemon get Gigantamax is limited to Gen I and Gen VIII. Yes, Garbodor and Melmetal are an exception, that doesn't remedy the issue but, if anything, essentiates it.
- Dynamax making the Pokemon giant loses its novelty fast, unfortunately the time spent to do all the animations doesn't go away with it.
Obviously all of this is of personally opinion... BUT I HARD disagree Megas were a lazy addition. Infact, quite the opposite, Megas probably took a lot of time to develop as they would likely need to go through the same steps a normal Pokemon needs to go through as they individualized their stats & other changes. The problem with Megas isn't the amount of effort put into them, but rather their limitation that the only Pokemon that benefits from the mechanic are the ones that got a Mega which were only 48/50 of them (which is still a nice number spanning across multiple generations, but still only them among the other 700+ Pokemon at that time; or rather their final stages within that number).
Now you'd then think laziest would then go to Z-Moves since they simplified things down to just one super attack. BUT, that said, they did really put a lot of effort into the Z-Move animations, especially the Signature Z-Move animations where they got the Pokemon model itself doing more dynamic movement only made for its model to look proper doing.
Nope, in my opinion, laziest award goes to Dynamax & Gigantamax. ~Ooh, they made the Pokemon model bigger!~ ... Yet it still does all the same animations as when it was smaller. The Max Moves also look like they have less pizzazz than the Z-Moves, ESPECIALLY the G-Max Moves which are just the Max Moves of their Type but with some additional effects. And though Gigantamax go through a form change, all they are is Dynamax Pokemon with a special G-Max Move which may or may not be better than the normal Max Move of that Type. Maybe if they at least changed their Ability to one better (or one that works while Gigantamax) that would have also been something but NOPE. Finally, I find the aesthetic only to be a bit creative due to them finding large things to turn the Pokemon into, but I find the Mega Evolution aesthetic of it being the "next step/super form" of that Pokemon feeling more natural (or at the very least less silly).