I'm intrigued that he beats Yukimura. The part about him being Tezuka's goal is understood, but what about this somehow enabling Yukimura to become even better? To quote the spectators in PoT: "My god, is this really (junior) high school tennis?!!"

That's exactly what I thought when I was reading. I can take that Fuji is good, no, excelent, but that doesn't mean he is better than Yukimura. Or, that Yukimura uncontiosly wasn't doing the same thing that Fuji used to do: restrain himself to give the other the chance to see what he could be. (here I am again, not making any sence)
And, after that, Yukimura isn't back for too long...his strengh isn't the same as before or as someone who is playing all this time he was in the hospital, so...after this game, he can improve much more, even more than Fuji, because used all his strengh as a tensai, and Yukimura can grow up yet. I mean, I believe Fuji using his real power can improve, but not so much, because that's his power, but the others can improve much more, because they are still growing up.
(I swear, after this, I'll stop to try to put my thoughts in words, because it's never works as it should work).