tt with 38mm was mich slower than it is now.
It’s true that a 38mm ball has less friction in air vs a 40mm ball and therrfore is quicker when Struck exactly the Same, but the 40mm ball has mich less spin and Therefore you can hit much stronger, ending in quicker Balls overall.
Just watch 38mm ball Games like wlq vs ma lin. In comparison to todays games, they were awkwardly slow, because the ball had so much spin and they were not able to hit it
https://www.tabletennisdaily.com/forum/topics/matthew-syed.13941/
Every time someone repeats this opinion, I show this video.
Kong Linghui at his awesome best yes. But Matt Syed was WR in top50 and one of the top defenders of the period. Notice how close to the ball was Syed yet the ball either went through him or by him without Syed getting close. The combination of 38mm ball and boosted bats spelt the end for defenders.
I don't know how old you are, but immediately the 40mm ball was introduced, the number of exchanges per rally significantly increased at all levels. For suddenly, even me at my very low level could stand closer to the table and retrieve balls that I could not get to previously.
Spin was also greatly reduced with the 40mm ball making serves easier to return. And so on.
Table tennis in the nineties was dying. One of the big reasons was that the balls during a rally (at all levels) was so fast, that each rally tactic was about who could drive or loop the ball first. That first drive or loop usually was the end of the rally. It was so very boring that TV networks stopped showing TT.
To this day, TT has not recovered.