I think this actually shows how solid in the market he is. I don't understand people who criticise him for "bringing in crap" like Alcaraz and McGeady. I will admit not all of his buys have been great but the ones that have been poor cost practically nothing. What sort of expectations do you have for a 4th string CB you bring in on a free?
Here are what I would classify as poor buys (even if the idea might have been sound, but it did not work out): Alcaraz, Stanek, McGeady, Atsu, Traore, Kone, Rodriguez, Stanek, E'too. Total spent ~ 12M (?) with 7.5 being Kone.
For all of those poor buys, Lennon, Cleverly, Robles & Galloway are in the same category (cheap speculative) and their success outweighs the flops of the others IMO.
Now look at when Roberto spends money in the market and his success rate.
Lukaku (28M) - great buy
Barry (3M+loan) - great buy
McCarthy - (13M) - great Buy
Funes Mori (9M) - Still adjusting to the league but does not look out of place in the PL. He has had a few mistakes but he has also been our best defender in some games as well. Looking like a good buy but still with room for improvement.
Besic (4M) - Still early but looks like to have the quality to be a PL starter
Deulofeu (4M) - Fantastic bang for the buck. He is also a player who certainly would never be in Everton blue if Martinez was not our manager.
Note: Too soon to make a determination on Holgate, Tarashaj and Niasse.
If you break it down, RM really has not had much money to spend especially when a lot of purchases are being subsidized by selling of Fellaini, Jelavic, Anichebe. I trust Martinez with a big war chest in the summer. Even if he does not fixes his issues next season and gets the sack, I have faith that he will leave behind players of value that managers will want to coach or at least have some resale value.