Actually there is a comparison...
http://www.telegraph.co.uk/sport/fo...pending-from-the-200001-season-to-201112.html
For the last 3 years net transfer and wages we have had higher wages but have done better on transfers, in total we are very similar.
Wages are an infinitely better comparison for how well a team does. There is a reason why low net spend Arsenal, spending £143mil last season in wages, beat everyone below them so easily.
Wages are long term spending that is fairly stable part of the club. Everton could get Fellani on a free one season, or pay £30mil the next, either way he'd get paid about the same wage. Transfer fee's are situational, volatile and a useless indicator of quality or how a team is competitive or not and on top of that those graphs are horrendously poorly made.
Wigans bar with £7.5mil net spend and £40mil wages, or £47.5mil total, is BIGGER than Everton with a £60mil wage spend and -1.7mil net spend, so the £47.5mil bar is BIGGER than the 58.3mil bar.......
Everton have a 50% bigger wage bill, and you buy and sell players based on the wages you can sustain, Everton have significantly outspent Wigan and there is absolutely no comparison at all. Martinez actually bought a few decent defenders, he lost 2 cb's for significant portions of the season and Figueroa for the last few games, and that guy is a freaking beast and a great left back. ULtimately though, you have CB's you can't get rid of, and have to buy new ones with minimal cost and ones with no money.
He spent more on attackers because goals ARE more important than defence and he couldn't afford both. If he spent more on CB's which he could have done, he might have had a better defence, but he wouldn't have been able to afford Kone, its swings and roundabouts. Arsenal can afford quality anywhere on the pitch, City can afford multiple quality players anywhere on the pitch, Everton can just about squeak in quality anywhere it chooses, the Wigans, Hulls and other small teams with no cash have to pick and choose where to fight, where to spend the money. THe team spent pretty heavily and got into some fairly serious debt BEFORE he joined and they've been rolling back the wages and spending since he joined.
Does that mean he'll do well at Everton, no, it just means how he did at Wigan has realistically no bearing on how he'd do at Everton. He might do better or worse with a bigger budget, he may do better or worse with a bigger squad and more people deserving games, he may do better or worse with more pressure, etc, etc.