Well during 'Super' MON's time at Villa, the only Prem club that spent more money were Man City. I'm not sure whether that's a combination of transfer fees and wages, or just transfer fees I just read it in a BBC article. But MON did sign some real shite (Reo-Coker, Marlon Harewood, Curtis Davies,
etc.) on high wages that Villa had to carry on paying for after he quit 3 days before the start of a new season. Milner and Barry got sold to Man City. Well it's hard for even a club in the top 4 like Arsenal to stop their players going there if Man City come calling. At least Wenger didn't quit at the start of this season when he lost Nasri to Man City though. And trust me no Villa fan (apart from a few oddballs maybe) would have been calling for MON to be sacked had he not got Villa in the top 4 etc. after losing Milner (still just one player, and it's not like Milner is Messi), I mean in terms of your 'ridiculous expectations' comment.
Anyway, most Villa fans including me were disappointed when O'Neill left, and he did v well in terms of results, remember his time at Villa fondly but he did not spend well overall.