I pretty much agree. I think O'Neill did well for us to consistently achieve 6th place. I think Hughes would do the same (the goalposts have moved slightly so 6th under MON may now be 6th~8th). That's by no means poor for us, if Hughes comes in and does that I think he'll be doing a good job.
But a 'special' appointment, someone like Deschamps, could possibly just move us on beyond that level. He made the perennial losers Marseilles into Champions and took Monaco beyond their level, he's a coach than can move clubs on a level. O'Neill, Hughes, maybe Moyes as well, for me are coaches that will take Villa to a decent level, do a good job but will never be able to move us on that extra step.