I'd say no.
Sunak is a member of the establishment and managerial class without any strong ideology at his core (even less than Cameron) however he is largely paying the price for inheriting a party that was already not unified and beset with the usual issues that plague governments in power a long time, namely that newly elected talent sits behind those elected previously that recycle roles but have long since engaged in their actual pasion projects.
Mainly though, as bad as a lack of direction and mild corruption and tiredness is, Sunak is ultimately paying the price for the fact that we saw a political reallignment in 2016 and only 139 Tory MP's joined parliament in 2017 and 2019, hence more than 200 MP's are from prior elections and while not all are out of step with the new reallignment, nor are they really in tune. In addition, when MP's do not believe a leader can win, they tend not to obey.
While not the same situation that Brown saw i think it's worth remembering that towards the end we had the expenses scandal and there was unhapiness in the party. I tend to think it will always happen to some degree if the same establishment remains in power.
Moreover, i don't think any other leader would be any better given the circumstances.