I don't have a strong view on Rabiot but I think he is our best midfielder to be honest - at least that was the case last year (Fagioli was suspended for most of it so who knows).
Just remember. IF Rabiot was on a contract somewhere else, even at the age of 29, his contract would be worth 30-40m and his salary would be around 5m. So for reference, Koopmeiners would cost 45m (on a 4 or 5 year contract) and come with a 4-5m in net salary - that costs the P&L ~19-20m per year. Rabiot just costs 14m. I know they are very different types of midfielders but you can see the rationale. And we no longer need to pay amortization on Rabiot's contract when he was purchased too.