I’m not disputing any of this, however a lot of this is balanced by the fact that babies have to learn how to learn and what language is. You do not.

If you moved to China, and your full time job was learning Chinese, and also your household chores were taken care of so you could focus on learning Chinese, by the end of the year you would be better at Chinese than a 3 or 4 year old born in China. You have a base understanding of how language works and don’t have to relearn the existence of grammar and sentence structure.

If you and your 7 year old child were both put in that environment, the child would probably learn faster than you, I won’t dispute that. But the larger limiting factor is time spent.