You have to play all the gens
But it was silly to introduce them if they are not going to continue with them. Many people just want mega evolutions, gym leaders and more of the same more or less. People don't want them to get crazy with all these new moves and shi-t. We already know how they work, if they are able to be used in competitive matches then battling just got even more complicated than it already is.
But no-oneeeeeeeeeeeeeee wants a replacement for gyms argh. Why change something that works? Look at the the comments, people would have been happier with lots of mega evolution and the same basic concept of the storyline. That's what the whole anime is about so to change it now is silly. you catch pokemon, you train and raise them, you beat the gyms and the E4, you get to be champion everyone's happy, sales go through the roof and we all live happily ever after.
They could have just refreshed them by giving them mega evo's. Sure the NFE's would miss out bo so what? If we got a mega flygon instead of a alohan charizard or something people would like that much better. Guarantee it. Plus darwinisms states the whole survival of the fittest things so it makes sense only the strongest/fully evolved pokemon should be able to mega evole or take on different forms. Not some baby pidgey in the ecosystem.