Indeed. He signed no defender of note who came close to being considered a decent signing - even their club captain he brought in was utter gash.
Moyes brought in players for low fees or from obscure locations and they turned out to be gems. Martinez didn't. The stature of the club barely matters with such players - one manager signed Seamus Coleman; the other Gary Caldwell.
Martinez's spending for players in during his time at Wigan was:
09/10 - 6.7 mil
10/11 - 9.1 mil
11/12 - 8 mil
12/13 - 8.3 mil
That's not even net spend either, in all of those seasons they received more money from player sales. So let's consider some of
Moyes's good defensive signings:
Lescott - 5 mil (in total)
Jagielka - 4 mil
Baines - 6 mil (in total)
Stones - 3 mil
Oviedo - 5 mil
All of which would have been a considerable amount of Wigan's budget, the most Martinez spent on a single player in his time at Wigan was 6.5 mil. Granted no-one can deny 60k Coleman is incredible but it's an outlier, even by
Moyes's impressive transfer standards while at Everton.
With that said, Martinez has only signed two defenders for Everton thus far. Alcaraz which was a failure, and Galloway, while he looks a decent prospect he's still unproven so I can't really comment on that. So the jury is very much still out, but I think directly comparing signings between Everton and Wigan is somewhat unfair.