I don't know, it's difficult to compare because they are different players (Strootman is a deep lying playmaker, MVG is an athletic b2b player) and Strootman is pretty much an elite player already. Strootman was already very established in the Eredivisie and his quality was obvious, whilst MVG has not reached his potential yet. Sure, one might be able to say that if MVG keeps progressing and sees off that horrendous injury he suffered last year, he might potentially become an excellent player because he has a very, very high ceiling (no real weakness in his game unlike Strootman who isn't as athletic) but Strootman is already at a very high level and will also only improve. MVG is a very interesting player because he can be a complete midfielder if he continues to develop nicely but there are too many unknown variables in football for anyone to say he'll be better than Strootman. Especially since Strootman is already a top player, who has a whole NT built around him. We won't ever know in the near future IMO, it's like comparing a prime Pirlo with Vidal, different players + also the fact that they're at different stages of their development.