The other question is a person has to ask is how much more unbeatable can you be than Tilden, since he almost never lost in his best years and won every major he played in? I don't think it's possible to do better. He only started losing (not much by the way) until he hurt his knee badly in a Davis Cup match in 1926. At that he was beating top players like Vines, Perry, Budge, Nusslein and Cochet into the 1930's and beat Ted Schroeder in a match in the 1940's.
I have my doubts whether any player could do better than Tilden in those days if whether you magically transported them from the 2010's or 1950's to the 1920's to play.
The problem is that during his peak (1920-1925), he largely only entered the US Nationals, of the major championships.
Yes, he won it every year (usually only having to beat minor greats like Johnston), but would he have won every other major, if he had entered them during that period? I have severe doubts in particular whether he would have won Roland Garros.
By the way, when the Musketeers came on the scene, they regularly defeated him, as can be seen from his sequence of defeats below:
1927 French: Lacoste
1927 Wimbledon: Cochet
1927 US: Lacoste
1928 Wimbledon: Lacoste
1929 French: Lacoste
1929 Wimbledon: Cochet
1929 US: N/A (Champion)
1930 French: Cochet
1930 Wimbledon: N/A (Champion)
1930 US: Doeg or Shields (full draw not online)
I know he was getting old by this point, and maybe he would have done better if he'd been a bit younger.
The point is though, Tilden's great success came when the field was weak and there were no other true greats to challenge him. When greats did come along in the form of the Musketeers, they often got the better of Big Bill.