Totally of the same persuasion as you, I'll say I did hear a very good counter point when Magnus Carlsen said in an interview at 30 he feels he can't compute lines as deep as he could previously, and his edge is now his experience. That was rather convincing.

Most of the folklore around "neuroplasticity" I've found pretty underwhelming. But yeah, if even he says it at that level of consistent practice, that seems like a good yardstick.