What Thomas Frank has overachieved with Brentford, consistently working with the lowest budget even during their time in the Championship, is probably the highest level that can realistically be reached under those conditions. I can't see him doing better than 8th place with the second-lowest budget in the league, so it makes complete sense that he would be looking to take the next step up.
People also tend to forget that Brentford have had several seasons decimated by injuries, and Toney's ban was a major blow. Yet, unlike Ange, Frank didn’t use any of it as an excuse. He adapted and dealt with the challenges head-on.
The real question is whether he could thrive at a club where both the board and the fans demand instant results, and the margin for error is razor-thin before things turn toxic. Personally, I don’t think he would.
Unless his agent negotiated a golden termination clause, I’m not sure I’d take the job if I were him.