Honestly that is probably the one big fault of Puyo Puyo: Puyo Puyo Tsu (and onward) has an obscenely challenging learning curve which will undoubtedly have one plateauing a lot. If you want to be able to make larger chains you need to learn how to build transitions. But if you want to build large chains in actual matches with an opponent who is good enough to watch your board, you also need to be able to build transitions safely and efficiently, which is why a lot of people do GTR as soon as possible. It took me a few years to get to a point where I felt basically just mediocre, and then I plateaued hard. To get better I'd undoubtedly need to hone my muscle memory for how to more efficiently use pieces and build more parts of the chain at once without breaking it or leaving myself vulnerable. I don't think I'll ever be all that great, but it was a lot of fun.
I played a decent amount of Puyo Puyo back in the day (mostly Tsu), but lost interest for two reasons:
1.) I had nobody to play against, and the AI in the old games wasn't very good. Neither of these are issues now though, with online play and much better AI.
2.) I could never get past the beginner phase. Making 4-5 chains really fast was usually good enough to beat the AI in the old versions, so I stagnated there. But that doesn't work against modern AI, and certainly not against humans. But I had no idea how to make the jump from beginner to intermediate; strategy just felt fundamentally different, and hard for me to figure out. Maybe I just never found good resources for learning that (this was 20+ years ago, probably much more out there now).
But yeah, it's a shame it never really took off in the west. Highly underrated game.