We can't buy Rabiot, PSG won't deal with us after Coman. They seem to be a very proud ownership. Forget about Lavezz, Pastore, etc.
Now we don't have any grounds to claim Rabiot is more talented than Coman. They play in different positions, this may explain why Rabiot was more used. Squad has different needs. Also if I'm not mistaken Rabiot is 1 yr older. Finally as far as I know PSG tried till the end to extend with Coman but couldn't. They learned their lesson and now they know the same will happen to Rabbiot, they'll just bag a few mil for him. Nothing related to talent.