Azzurri, this does look like a contradiction, and it's not getting any clearer.
Whether you bring today's players to the past, or the past players to the future, you've got the same problem: you haven't seen the older players.
That's the reason you gave for not wanting to imagine the modern players in the 1940s. Fine, you don't want to pit them against players you've never seen, in conditions you've never witnessed. But these same players you've never seen, you're willing to judge that they would not adapt well to modern conditions. You know next to nothing about how these players adapted to their own conditions, nothing about what specific similarities might exist between their conditions and ours -- but nevertheless you're sure that they would not adapt well.
In another post you said it's clear that tennis is very different today. Very true, but if that's your point, then today's players are going to face very different conditions in the past. That's at least a great challenge for them -- but you won't even touch that question. It's hard to see why. Seriously, you don't need to see anyone play -- you don't even need to see one minute of old reels -- to know that changes in the sport over time are going to challenge any "time traveler" in either direction.
I'm surprised you thought only the "clueless" would see a double standard here. The problems you have with comparisons -- you mentioned the changes in technology, and lack of knowledge about older players due to limited footage -- cut both ways when comparing generations. But you've only cut in one direction.
On the one hand, Pancho was not born in this era. So no judgments are possible, you say, about how he would do with newer technology. But the 90s players, you're convinced, would do great if we gave them newer technology.
If the reason for your confidence is that you've actually seen the 90s players, I get that. But then I don't see you anywhere suspending judgment about how older players would adapt to new technology. To the contrary you've said everywhere that they would be destroyed.
Everything that you know about the past eras of tennis comes from short film reels about as long as YouTube clips, and from historians, which technically is "word of mouth" - though I would not call it that; otherwise we could never do history about anything.