I just get a bit fed up with everyone slagging the guy off prematurely
I'm with you there. I think he's done creditably, maybe even better than creditably. I'm also in favor of continuity. It's very easy to want to sack the manager if you're not doing well (or, in our case, are doing well, but aren't playing attractively). But sacking managers is not a recipe for success. Quite the opposite.
I might guess that AVB has exactly two seasons, this one and next one, to get us a CL spot. Who knows if that's right, but (considering how new a squad he has this year), that seems reasonable. That will also have been a decent interval of three years with him in charge. The best available managers will be interested in the job, if it does become available.
Sack AVB now, or even at the end of this year, and I think a lot of the best managers will say, poisoned chalice. Of course, Harry would probably be available, at least until England or some other job he prefers opens up.