I agree with your post about Professor Oak and Sycamore. But I get the feeling they didn't want to have Oak cameo in X/Y because they might think that if they did, we would all assume that Kalos isn't as far off from the other regions as they supposedly say. And then they'd get people like myself at least, wondering when they'll stop pussy-footing around and just give us a game where we can travel the pokemon world all in one game.
It’s not even that, though. Instead of having your friend, Tierno, give you the Kalos region starters, it should have been Sycamore. Sycamore is so distanced from the Kalos region starters and yet closely tied to the Kanto region starters, it’s so easy to forget that he specifically trained the Kalos starters for you (trained is used loosely here, since, they’re level 5 with no exp, no EVs/IVs breeding, and no egg moves). His ownership of the Kanto starters is happen-stance.
Furthermore, Sycamore seems like the least interesting professor in terms of research. He feels more social than investigative. Sure, he’s tied to the Mega Ring, Mega Evolution, and Mega Stones, but there are other NPCs who give just as much information. In fact, your group of friends deliver more info about Mega Evolution compared to Sycamore; Gurkinn and Korrina do all the muscle when it comes to explaining and distributing anything about Mega Evolution.
Sycamore, while suspicious of Lysandre, does even less to stop him. He appears once everything comes to light, and just points out how he was suspicious of him (also, it feels like he sympathizes with him). I know, but no other professor gets that involved! This was a chance for Gamefreak to create a dynamic professor, a great NPC who was just as important as you, but instead, they creates a boring, social character, who just hands out freebies. Oak started the ‘dex, Elm researched breeding, Birch studied habitats, Rowan focused on evolution, and Juniper specializes in origins. Sycamore, I guess, deals with Mega Evolution, but it’s so minuscule. Like, Birch was the least involved of the professors, basically only having the task of starting your journey, but his story lends to his lack of involvement with his field research.
Don’t get me wrong, Sycamore has a great design and he’s a lot more appealing in the anime than the game. I understand that his great design is what many people like. I get the appeal, too. I was the same way with Juniper, mainly because I was beyond excited that a female was a professor (plus, she’s as involved as Cynthia was in Generation IV). I just wish they tied him to Kalos better. He’s as much of a disposable NPC as Diantha is as a champion.