He did work under restrictions, could he have came in an bought 18 new players like Koeman expects to??
He only wanted one last year, Yarmalenko, who would have addressed a massive hole in our team now yet we couldn't afford to take that happen.
The fees you mentioned are nominal for Alcatraz who was an ok 4th choice and 250k for McGeady who Moyes tried to sign as there was players who potentially could do a job, on the cheap, and had played at quite a high level. Filling the squad with players like this allowed us to sign Lukaku who we'll sell 80 million.
Give Koeman 17 mill a season to spend as you say and he'd walk out on us. Not that he had 17 million per season as the inflated fees for Niasse and RFM are all clause related but that's another argument.