Megas are the best thing GF ever made. The only problem is some of them, like, less than 5, that are too strong. Otherwise, everyone else is fine.
>it made more already strong Pokémon stronger
Overall, it didnt. Strong stuff like Garchomp, Tyranitar, Gyarados, Scizor mostly got a sidegrade, and sometimes their Megas are not even better than the regular forms. Meanwhile, Charizard, Pidgeot. Beedrill, Kanga, Pinsir, Manectric, Aggron, Lopunny, Mawile, Altaria, Sharpedo, Swampert and more are all improvments.
The decision of which pokemons should have Megas went well, too. Popular Pokémon, shit or not got megas. Shitmon got megas as well and mostly became good. Legendaries are pointless, most of them cant even be used anyways, but they are popular, so they deserve it too.
Evolutions cannot be given for everything. 3rd stages and stuff that can abuse eviolite, for example. Best choice for them are obviously the Megas.
But go ahead, keep eating the Gen 1 only Alola forms that mostly dont look strong, only pretty, instead of wanting your Pokémon from other gen to get a upgrade, since Megas are for every gen.
Or even worse, a 5th move bs that no one asked and thats only going to give more coverage for stuff that shouldnt get it.