I will leave people to assess your insight from what you have posted and whether world ranking is the best way to measure whether Quadri and Dima and CCY were still playing high level TT into their 30s. But anyone claiming that random top 200 players can beat 2700+ players is not worth seriously debating - anyone can lose to anyone because people are human beings, but it's almost never random and hard to understand without knowing the players.
Kou Lei could easily compete internationally if he was motivated, he isn't that much worse than Ma Jinbao, who is competing very well on the international tour and Lou Lei is at least as good at Yaroslav Zhmudenko who played in the Olympics for Ukraine - you may not remember that Kou Lei was US Open champ in 2022 just two years ago. Some people just don't think there is enough money in TT and they don't have the mindset to just put themselves through the hustle when they make great money coaching and that is okay for them.
My point here is while MLTT isn't close to the top league in the world, anyone saying it isn't a high level league requires context and sounds more like youtube CNT fanboism where you can just say well, the players are not all TTR 2500+, so it is a B-Tier league. In reality, not everyone wants to sweat all day long fighting internationally with no real reward. Lebesson isnt really past his prime, he just has has too many better players in front of him in the French national team. Koki Niwa suffered from exactly the same issue and retired for the same reason, but even in his prime, he would have stood no chance against the current generation of TT players. Satoshi Aida, who is supposedly well past his prime, is still able to place in the Japanese national championships - so what was he doing at his prime, leaping tall buildings in a single bound? Provost was just a couple of years ago making the semis at the French Nationals.
In any case, if your A-tier is just CSL, French and German, yes of course, MLTT is not an A tier league. But I am arguing that your concept of A-tier league is YouTube driven and has little to do with the reality of competitive table tennis. Many strong players in the world don't play in the first division of CSL, France or Germany.