This is an impossible scenario: first of all he'd not even get to face the top 4 if everyone else beat him easily. Besides, if a certain game was effective against the top 4 but easy pickings for the rest of the field, we'd have like the weakest top 4 in history, no?
Well, it can't be literally everyone because he would need some wins to have a ranking in the first place. But he could stay in the top 100 by 'vulturing' challengers, and meet the 'big 4' in R1.
As to the second part, let's say he's a 'Gulbis' type. He has no real motivation to play tennis, unless it's against the top 4, where he plays out of his mind. But he'll always lack the commitment to do any better. Is he the fifth best player in the world?