You just need to look at the funds available;
Signings over 10mil made under Martinez -- Lukaku, McCarthy, Niasse (Mori was 9.5mil but a 50% profit could have been made on him too).
Lukaku was a major success
McCarthy would have been a success but for injuries and was heavily linked to Arsenal.
Signings over 10mil made under Koeman -- Schneiderlin, Bolasie, Williams, Klaassen, Keane, Pickford, Sigurdsson.
Pickford has been a major success.
Signings over 10mil made under Allardyce -- Tosun, Walcott.
Jury is out.
Quite clearly Martinez spent larger transfer fees far more wisely than Koeman.
I think if Martinez was given the 190mil Koeman spent on those 7 signings above he would have theoretically signed superior players to fit into his system and would therefore have had far greater success.
Add on the 50mil odd Allardyce has spent on two players who wouldn't be first choices in the top 6 and its hard to argue against that.