I don't think he underestimated the PL, but the Man City takeover has moved the goalposts a fair bit. I do think he overestimated O'Neill's ability to spend his money wisely.
We get hammered by Man City 4-0 , they look like now adding Dzeko to their squad. If I was Randy , I would be giving in , which is sad but this is what footballs has now become. how can teams compete?
I also dont think he underestimated it and the size of the job he took on when he brought us he had a five year plan and now things have changed i think he is starting to see how difficult the premier league can be.
settle for eternal mid table mediocrity.