Boom-Boom
Legend
I didn't think the question the OP presented was "who's better or greater" but simply why Becker had a clear (even dominant the case of Edberg) winning h2h against Wilander and Edberg outside of the biggest events, but within the biggest events, he had a losing record, an even record, or at least a much less dominant record (depending on what you include as "biggest" events).
I actually don't think there's much of a clear reason. Many of those big event losses to Wilander and Edberg could have gone the other way with becker winning. And, even if you think Becker is better or greater, it's not like we're talking about two average opponents. It's Wilander and Edberg for goodness sake. Yes, they have losing h2hs vs. Becker, but obviously they are great players in their own right and clearly had the ability to beat Becker on any given day. So happens that those "given days" happened to come on big stages.
And Becker had a lot of indoor wins over Edberg (including some DC beatdowns), which helps explain somewhat his big overall h2h. I mean, Edberg was excellent indoors as well, but Becker may be among the best ever.
Yep my theory re Becker defeats at Wim and WTF against Edberg particularly has always been over-confidence. Becker clearly felt superior to Edberg (probably cos of the overall H2H) and didn't come in the right fighter mind on those occasions except in Wim 89 with that bagel in the first set and 3 setter win, only to come back to over confidence/arrogance in 1990.
With Wilander it's a different story, clearly an horrible matchup for BB to play Wilander on clay, especially before 1990.