Remarkably reductive logic.
Moyes found Everton in the gutter. They were on the rocks financially and their Chair had started selling players behind Walter Smith's back to keep the banks off. They'd finished in the top half of the table once in 10 years, their previous 5 finishes were 17th, 14th, 13th, 16th, 15th. It looked inevitable that they'd get relegated and the season that Moyes took over looked like being it.
Instead he kept them safe, then over the next 10 years only finished in the bottom half of the table twice, with his last 5 finishes 5th, 8th 7th, 7th, 6th. I think its totally fair to say that Moyes saved Everton. Had they been relegated, given their perilous financial position in those days, they could have been facing years in the wilderness of the lower leagues. Instead he rebuilt the club and assembled a team of players that were able to take the club to the cusp of challenging the big boys, trying to compete with clubs with double the spending power.
Just because Martinez has been able to pick up the reigns, add his stamp and move them forward doesn't take away from what Moyes did in any way. That Martinez was able to pick up that Everton team and challenge the top 4 is credit to Moyes. Do you think he could have done that had he taken them over in the relegation zone as Moyes did?
History certainly suggests not. Martinez took a team in Wigan that had finished 10th, 17th, 14th and 11th in their first four years, then proceeded to lead them to finish 16th, 16th, 15th and 18th, ending of course in relegation. Martinez is building on the foundations Moyes built.
So does that mean Moyes is better than? Course not. Different managers are right for different clubs at different times. Moyes did outstandingly well at Everton, Martinez has done too.