Tezuka at that point do not have Saiki, Zero Shiki Serve, nor Tezuka Phantom. All of which should be add to his technique. And those techniques all raise Tezuka scariness immensely. And Tezuka did not use Hyakuren in those 4 game that he won either. So more technique could be subtracted from that. If fact, Tezuka doesn't even use Tezuka Zone is those 4 game.
I don't see how that's relevant. There's nothing to suggest that special moves are factored into the stat sheets. Miyako and Krauser both have 5 power, they don't send people flying with normal hits, but Krauser can do it because of a special move. Nakagauchi has 5 technique (most likely) due to his ability to target his shots perfectly, no special moves at all.
In other words, there's nothing to suggest that Tezuka doesn't have 5 technique and 19 total without TZone, Hyakuren, Saiki. Furthermore I wasn't pitting Shiraishi against those moves to begin with.
If Fuji match with Tezuka were of any indication, that would suggests to me that Shiraishi can win this match too.
Fuji beat an illusion of Tezuka, not the real thing. He himself, Ryoma and Sanada all say that.
Nor doesn't anyone have any doubt 10 baller won't be able to beat Ochi, although master of return Yukimura say it's a ball that can't be return.
The main reason why we think it's easy for the G10 to break Mach is because Ohmagari called it a joke.
As for Neo Scud, Renji has already shown that he can beat Waterfall (which is only 3 kph slower) every time, and we also know that someone from 6th court managed to score against it at least once (Ootori's win afterwards is implied to be because his game outside of his serve, not the serve itself, improved), so while we can't say that every top tier character would beat Ootori 6-0, it is very likely that they will beat him.