An interesting question.
I looked back and it seems that we are the best in terms of midfielders when we play with La Masia or Spanish guys.
Our last xx central midfielders:
1. Andre Gomes, fail
2. Denis Suarez, fail
3. Arda, mostly fail
4. Rakitic, ok to good
5. Fabregas, average
6. Keita, ok for a sub
7. Van Bommel, average
8. DECO, awesome
9. Riquelme, fail
10. Fabio Rochemback, fail
11. Menieta, fail
12. Gerard Lopez, not good enough
13. Petit, fail
14. Litmanen, fail
15. Ronald De Boer, fail
16. COCU, good
17. LUCHO, good
So, in the last 20 years, we had tons of failed transfers of (central midfielders).
But players who were good, were domestic guys like: Pep, Lucho, Xavi, Iniesta.
Good transfers in the last 20 years were Lucho, Cocu, Deco and Rakitic.
This raises huge question marks over future expensive transfers like Bernardo Silva, Coutinho, Ozil, Pogba and similar.
Verratti would probably clicked well. But all other players (knowing our history), it is very questionable.
But still, Alena, Rafinha and similar guys seem like better fits than 40-50 M guys like Gomes and Arda, that's sure.