Not sure about this. To me it makes sense the best servers would have an advantage. They are far more likely to win service games to 0 or 15, after all. In a normal set that doesn't make any difference as holding your service games is all that counts, whether it's to 0 or to 30. But in a tie-breaker, if you're less likely to lose points on serve, that does make a difference as the breaker is a matter of points. Of course you could make the same case about the best returners, but even in today's conditions, the serve is more powerful than the return, and the best servers win more points on serve than the best returners on return.
If one player can consistently win a greater % of service and return points than another, they should be winning that match-up regardless of whether tie-breaks are required. It is very rare for a player to win a match in which they win less points than their opponent. We must not mix-up 'better servers', with 'better players'. You say it doesn't matter whether one holds to 0 or to 30, that's true. Over time though, it's the percentages that matter. A player who averages 30 in return games is winning 33.33% of return points. A player who averages zero is (obviously) winning 0% of return points. The first player will (usually) break serve at some stage, while the other player never will. I realise this is obvious, but it is necessary to understand this point. When Nadal/Djokovic/Murray plays a big server, the big server DOES NOT consistently hold serve more easily than they do. If they did, then they would hold an advantage over the match-up tout court
, not just if it reached a tie-break.
I mean, how on earth do you suggest the top of the game is dominated by great returners if you really believe that the big servers are both 'far more likely to win their service games to 0 or 15' AND hold an advantage in tie-breaks? The only plausible way this could take be consistent is if the good returners were always holding to 30 or to deuce, and then occasionally breaking whilst usually being shut out on return. Not only does this defy common sense, but it also is not borne out by evidence. When two players play, the one who wins the most points overall almost always wins. Winning the most points is a function of both serve and return, the EXACT SAME SKILLS that win points in a tie-break.