I'm actually giving it all the credit it deserves. Also Sakurai never said anything about adding the mascot of a generation. I wouldn't be surprised if Pokemon Company told him to include Genesect, because that's currently the character they are pushing. I think you are greatly underestimating Genesect's popularity. And a lot of us would like to see a new Pokemon instead of just veterans, even Sakurai would probably feel that he's not giving Pokemon a lot of love by just bringing back a Melee Veteran.
No, they're primarily pushing Mewtwo, Genesect's second to him (ok, her) but it's pretty obvious who their marketing darling is right now and who they'd pick if it came down to it first. Really, you seem to be overestimating Genesect's popularity, it's not nearly to the level of Mewtwo, Pikachu, Jigglypuff or even Lucario, especially at their primes.
Kind of like how Lucario was in the movie and he was the mascot of Gen 4?
And yet Lucario has been pushed even after his generation is over and still holds on to a strong, dedicated fanbase. That's popularity, if Genesect does the same then all the power to him but right now he doesn't compare to Lucario at his prime and we don't know how the future will affect his popularity.
Kefka is a better written character (joker is rarely written well)
and just going to say most people who like the "random kill every thing villain" are mostly 14 year olds
Do not do that, do not put down a group of people by saying their favorite character is only liked by "young kids/teens." On top of that, you have no basis for that point, no polls or otherwise to support it and really there's a lot of adults that do like the character so don't try to push your opinion as fact.