The reason your logical argument fails this time is what I like to call the Testud/Fernadez principle.
This rule holds that if a great player is only playing average tennis, even Sandrine Testud and Mary Jo Fernandez can beat them. That doesn't mean Testud or Mary Jo is the better player, does it?
A great player has to play good tennis to beat the players just below them.
The 'Testud/Fernandez' principle. I like that, even though it's completely unfair to Mary Jo, who did play three slam finals. She could beat great players who were playing well, but not 'great'. But it's a nice principle.
I think where I disagree with you is this. Great players can grind out matches against other top ten players when their playing BADLY. That was one reason I referenced Serena's perfomance in the 2005 OZ semi. (That's the match where the announcer said, in disbelief, that Sharapova was playing better, but somehow Serena was winning.) We also have to seperate great careers from great right now. Arguably, the only 'great' player on the tour right now is Serena. And you could argue their aren't ANY. Yes, Venus has had a great career
but I would argue she's only one of many 'very good' players right now.
I don't look at Peak as playing their absolute best. Peak for me is when all their shots are working and they are playing what for them is "winning tennis".
Interesting. When I think of peak, I pretty much think of the best they can play. Serena in the 2007 OZ final. Hingis in the 1997 OZ final. When I think 'peak', I think 'in the zone'.
In most cases, to me, you don't see 'peak' vs 'peak' matches because generally a great player, at their best, negates the other. The Wimbledon men's final this year was probably as good as both those guys can play. Memory may lend rose colored glasses, but Seles and Graf played a couple of times when they both really had it dialed in.
Ultimately though, that might be the biggest problem with words like 'peak', 'in-form', and 'A-game'. Their imprecision. Your definition would fine, if everyone understood and used the term that way. But reading the threads, I don't think they do.