What does the X570 PLUS lack that you feel you will need down the line?
Futureproofing is often just code for spending money for no actual benefit - because by the time the future is here, anything you bought today would have been superseded.
I only play a few games in the list above but from youtube vids etc there seems to be no difference except a small fps boost of around 3-5 with the intel
That's what I said. In most games there will be little difference. Most of the games in the article I linked show little difference. But you get the odd outlier that does show a difference.
You said you don't want to compromise framerate. If that's the case, get the i9 10900k. If that's not really the case, in that you want good performance but don't want to sink even more money into the system, the R9 3900x is fine for gaming, and very good for the other non-gaming uses you've previously mentioned.
It's not a question any 'expert' can answer for you. The facts are that the R9 3900x is close in most realistic gaming scenarios, but the 10900k is technically better, and meaningfully better in some titles that show more of a difference. The question you need answering is whether that's worth spending more for to you, which is between you and your wallet.