According to the table on this website Rotherham's budget was the third lowest in the Championship. It was quite a bit higher than Wycombe's and marginally higher than Coventry's. It was, however only about one third of Derby's and less than a quarter of Sheffield Wednesday's:
https://outsidergaming.com/football-...for-all-clubs/
So all things being equal, Rotherham should have been relegated 3rd from the bottom. Thus by that measurement Paul underperformed by one point and Gareth Ainsworth overperformed by 2 points. And Mark Robins over-performed by 13 points.
Of course that is not the whole story because Coventry and Wycombe did not have to play the absurd number of games Rotherham had to play in a relatively short period at the end of the season. Mark Robins incidentally did not get Rotherham promoted at the first attempt and, according to the data I cited (I can't remember), we were relegated the first season he was in charge and the second season he was in charge we were only in the 4th tier but he still didn't manage to do once what Paul Warne did twice in the 3rd tier i.e. bounce back promotion.