It's not about dexit, it's about long-term thinking and efficiency. Gen 5 wasn't hated for that reason. People, like me, thought that Alomomola IS the evolution of Luvdisc, and, like Bouffalant (as an evo. for Tauros) and Maractus (as an evo. for Cacnea), they just wasted those Pokemon.
Up until gen. 5, people were expecting for new evolutions of older Pokemon, and with each new generation that was announced, people had their wishlist for which Pokemon they want to have an evolution. Ever since gen. 5, there are barely such Pokemon - 0 in gen. 5, 1 in gen. 6 (and only because of the introduction of fairy type), 0 in gen 7 and finally, when they made such new evolutions in gen. 8 they had to be "unique" and be a regional form evolution. Why is that for?
It seems they don't think "normal" evolutions are exciting, so they have to come with some new gimmick each generation - ME, regional form, Dynamax... and those are all one-gen gimmick, instead of normal evolutions that will last forever.
When they come back to redesign older Pokemon, and at the same time there are less new Pokemon, it gives the feeling that they don't have new ideas so let's just make Diglett a bit different and there we have it - a new Pokemon. Back then they used to tag those redesigns under special forms such as ME or regional form - but now they are going all the way and calling it a new Pokemon, although everyone knows - and they admit it - that it's some older Pokemon in disguise.
I dunno man, to me it just gives more diversity.
Mega Evolution: Although broken, gave the chance for people to use their favourites that might not be as strong be more viable as well as make stronger favourites even more stronger. Its fanservice ya, and broken, but it did the trick for making fans get excited about it.
They also added a lot to the lore and history of Kalos.
Regional Forms and Evolutions: You like Marowak or older Pokemon and not newer ones? Guess what, now you can have more of the same favorites but with different typings, abilities and movepools to make up a bigger team now. Don't like Sandslash, but what if it was Ice/Steel and looked like this? Now you like a Pokemon you never liked before. Regional Forms give options to fans, reworking older designs and expanding upon them, given them new life. You'll see many people say they don't like Meowth, but love Alolan Meowth or Galarian Meowth more. Also Regional Forms just add more to the environmental lore of regions and conceptually often tie older Pokemon closer to looking like they belong in newer regions. With Regional Evolutions, we get to see how because of the environment or differences make these Pokemon evolve further. Its not GameFreak giving up on older Pokemon who need evolutions, but making the decision that older ones that don't evolve just can't without these divergent evolutionary stepping stones. Like Corsola most definitely could not evolve into Cursola.
Plus Ursaluna, Wyrdeer, Kleavor and more to come have shown GameFreak have not given up on cross-gen evolutions.
Gigantamax Forms: Honestly just made secial visual spectacles out of some Pokemon to make them cooler, not a bad thing when trying to sell a gimmick.
Now with Wiglett, we get confirmation convergent evolution is a thing, a burrowing garden eel as evolved the same way to have similar traits as Diglett. That's pretty fun and Diglett fans get a whole new similar Pokemon to love. Again though, some people who don't like Diglett, now love Wiglett.
Like I said, adds diversity and options.
Also, people most definitely shitted on gen 5 Pokemon for just being the same animals or similar appearance to past Pokemon. People who saying the entire dex was just a worst version of gen 1. When gen 5 has some of the best designed dexes out there.
Also since forms seem to be no-no for you. Would like to know the total and what they are for this gen? Soften the blow or warm you up to the idea prior? I'll PM if interested.