To be clear, I agree 'greatest of all time' is pretty meaningless, which is why I have no stake in whether Ma Long or anyone else is or isn't.
Greatness has no real objective definition, it's IMO fairly pointless to discuss, it comes down to semantics in the end on what you mean by 'greatness'. But Ma Long, and likely some other modern players are probably going to be 'better players' by virtue of of being born and developed in a later, and consequently better time.
It's also unfortunate that table tennis happens to be a sport in which rules have changed so much in just the last few decades that were you to hypothetically have a time machine and set up a match between a modern player and a player from their past. The choice of ball, service rules and scoring system means they arn't even playing the same game the way they trained to play that game anymore.
But in a sport less wracked by fundamental changes. While "Greatness" is pretty meaningless, I think it's fairly clear Modern players are going to be on average BETTER than players from an older era. That is to say, in a sport that has still the same fundamental rules, if we were to use a time machine to set up the direct matchup, between a modern player and a player from an older time. The modern player would probably outperform them.
We'll take swimming as an example (it happens to best isolate the principle). Since if you take away advances in technology, it doesn't mean a modern swimmer is completely unable to function competitively, they are just a bit slower. With the adoption of the flip turn and the dolphin kick, the modern swimmer is obviously going to wipe the floor with a similarly ranked swimmer from before the 50s, despite swimming under the same rule set. That is to say, the modern swimmer is objectively better at the sport of competitive swimming, especially for short distances. Even without their fancy skinsuits and faster pools.
Sure, these improvements in technique, were invented by people in the past. But the fact of the matter is a modern swimmer/player benefits from knowledge of the past, it is a part of what they are as an athlete/player. It in no way stops the modern athlete from being better at their sport.
This is in no way meant as disrespectful to players, or people in general in the past. Or in any way diminishes their contributions. This is just how progress works. Future players will almost certainly be better players than the players of today.
If we arn't overall more capable than people of the past, then we've been doing this whole civilisation thing wrong.
