I do believe he's been a success and a hugely positive figure for the club, outstanding and massive may be going a little over the top though.
To give balance to your argument...In the current climate finishing third is meeting our objectives, it isn't similar to winning the title. And we did finish 4th last season behind Kilmarnock. We can't expect to finish above the OF but we can expect to have a level of consistency against the rest of the league which keeps us reasonably in touch. We can also expect that our efforts against those sides would be significantly better than they have been in our two pathetic attempts this season.
Cups have been positive in the number of finals/semi finals we've been in but there's been some noteable failures too.
But ultimately, he can't just be judged on historic achievements. He is the best we've had since Fergie but it's fair to say he is not performing to that level currently. It isn't healthy in any organisation for there to be a prevailing attitude of 'we can't do any better so we'll turn a blind eye to the fact they're under-performing'. People need incentivised to keep building on success.
I believe he can salvage it over time but others don't. There is no doubt things need to improve.