Do you think both would have had the same impact if they were switched? Keano was a great player but if he didn't have the stars/leaders around him like he did - would his style be too much? Could he have won matches on his own?
Same with Robbo - maybe he wouldn't stand out for his leadership so much if he had great players and leaders to win games? Ofcourse all this is hypothetical. They were the best at that time and exactly what we needed.
The most difficult thing to quantify about if they were switched is how each player would have dealt with the culture. Keane bought into Fergie's culture 100% and was instrumental in implementing it. Would he have been as effective under Big Ron? Hard to know but I don't think it would have suited him as well.
Saying that, it's really overstated the stars and leaders in the team when Keane was there. When Hughes, Ince and Kanchelskis left and the class of 92 came into the team, it is massively underplayed how key a role Keane played in that transition.
Having 3 of Beckham, Butt, Scholes and Giggs all in the midfield together at that stage was a massive gamble. They were amazing talents (apart from Butt who was solid) but young and inconsistent and the role Keane played in leading that midfield was incredible.
Robson didn't play with complete duffers either. Wilkins, Webb, Moses, Ince were all quality partners. Strachan, Olsen, Muhren, Whiteside, Sharpe, Wallace, Hughes, Stapleton, McGrath, etc. They were good players.
Robson was a fantastic individual and usually led by example and did it himself. Keane elevated others around him.
Keane showed he could elevate some pretty average players also. In qualifying for the 2002 world cup, the Ireland midfield was McAteer, Keane, Kinsella/Holland and Kilbane. They were genuinely impressive against Portugal and Dutch teams containing Figo, Rui Costa, Van Bommel, Cocu, Kluivert, Overmars, etc.
It's such a shame that Keane didn't get to play that world cup.