Under the surface, I don't believe most people who have raised doubts about Pardew are criticising his ability as a manager per se, rather they are highlighting that Pardew is a naturally cautious type of manager and perhaps what the club needs over the next 18 months+ is a more adventurous manager.
As I say, it's more an observations of styles of management rather than ability.
It may just be that Corteses has come to the conclusion that Pardew's 'style' doesn't quite fit the agressive success timescales being set. (even a 5 year 'bounce back' timeframe is ambitious)
IMHO, Pardew is a very good manager for consolidating a team's current position but not necessarily the best manager to get us up the ladder quickly.