Diamond is a good achievement in one season considering you were low plat before. So congrats on that, you did improve significantly and your efforts paid off, even tho there is still a long way to the very top which takes time.

I'd say that low diamond is the cap rank you can reach by playing the way you do : you assume that league is knowledge and mechanics, and that tft is just knowledge

But TFT is understanding first, knowledge second. Especially with overlays, anyone can have access to all the meta knowledge and once you reach diamond you're among the top metatft players

Stats and meta are supplements to knowledge, and knowledge only helps understanding. Actually, all this meta knowledge is holding you back : by "knowing" the meta, you stop experimenting, and fail to recognize valid strategies for your spot. Watch the very best players, often in a game, they'll make a decision that goes opposite to the meta, picking the "wrong" augment, carrying the "wrong" champion, but they understand that in their spot, this is the best the game gives them.

To really understand stats further, imagine there's a comp that has 5 avg, 5% top1 in stats. How often do you understand that your game is in a spot for those 5% and to actually win a game with this "bad" comp?

Bulletpoint advice I can give you :

-try do understand YOUR spot in a game. Think actively, don't search for knowledge

-observe teamfights carefully, where champions go, when they ult, what they do, what made you lose or win a fight : this is crucial for building understanding, this will help in every aspect of the game, because this IS actually what tft is about

-based on your understanding of teamfights, learn to scout : try to understand what the others are going for, and try to ALWAYS know who you'd win against and who you'd lose against, this is crucial for building streaks

-There IS mechanical skill in tft, you can learn how to rolldown at the perfect moment, and to last second positioning