Villa were a yo-yo side, could push for Europe or implode, that was down to poor managers. Certainly during the Premiership era they've been a club that should be top 6/8, with a solid fanbase and decent squads (Their Prem record backs this up, the only seasons they've finished out of the prem top 8 are 94, 95, 03, 05, 06, 07, the last being O'Neils first season)
O'Neil brought them stability, and consistency, however he's not really taken them up a gear beyond what they should've been achieving anyway. They've perennially had the squad thats said 'Europe is a must', yet he's never gone for the players that would try and push on.
As Marcotti says in the article above
he's bought British players, mostly young ones, for which he's been widely praised. But again, it's not as if he's unearthed gems, signing some teenage left back from Colchester who then goes on to become the next Stuart Pearce or an underrated striker from Reading whose career he helps get back on track. Most of his British signings are fairly obvious ones - well-known players at market prices, whether it's Stewart Downing or Ashley Young or James Milner. There's no great nous or imagination there, it's basically a case of bringing in brand names. And paying accordingly for the privilege
Not saying he's a bad manager, and I personally like him, but he's not exactly excelled at Villa. And pointing a finger at Lerner just deflects criticism for me, because his predecessors all had Deadly Doug as chairman, yet still managed the same......
Interestingly, I think O'Neil might be one of the few British bosses who'd work OK under the Continental system of being a first team coach, with a General Manager/Director of Football conducting transfers/scoutings.... So long as he had control over training/first XI/squad management, he'd do well with someone else giving him the players/future stars