I still don't understand how you are thinking that giving a older Gen Pokemon spotlight is better than giving a current Gen Pokemon spotlight.
Maybe I want to see some nostalgia out of Ash's pokemon, he's got so many pokemon now it's hard to see all of them get used equally anymore, and he just keeps stocking up that it makes investing intrest in the new guys pointless cause their going to end up like his old ones, and when a league comes around which is one of the few times they can get some exercise, people don't want them to come out for fear of taking glory from the new guys.
Except during filler arcs which lead to pointless goals that do not help Ash towards his endgame.
The reason why I want him to catch lucario is because I still believe it would fit him and can showcase quite a few Z-moves for him due to the versital moves it can learn, and I bet people would probably take that over the other fighting pokemon which people seem to be well fighting over quite abit.
Charizard and Sceptile have gotten plenty of spotlight beforehand, bringing them back would've taken away the spotlight from the current Gen Pokemon.
Because out of the pokemon that Ash had that could mega evolve those two made the most sense. Heracross and Jason didn't have near the level of bond those two did and Sceptile could've been for ORAS promotion.
Making a current Gen Pokemon the ace is reasonable, and thus, giving it a special transformation.
Making a current gen guy the ace is fine(hoping Litten is the Ace for Alola), giving it something it didn't need isn't.
A special transformation, which reflects the bond between Ash and Greninja, where it resembles Ash and they share each other's feelings- I can't see what's wrong with that.
It got triggered in nearly every freaking battle Ash and Greninja were involved in after it's first few inceptions and the one time he tried to trigger it by force, failed and got beaten by Sawyer's Sceptile.
this ain't DBZ, we didn't need to see it in every single fight, that made it less special.