The PLP composition hasn't changed AFAIK, and they are the ones who block/dither/force to u-turn on some reforms that the general population wants: immigration, budget, benefits, defence, etc. that won't change with Burnham, it will be even worse.
He ain't the best politician: he is not. Experienced, yes, but never a game changer. He retreated to Manchester after losing 2 leadership bids. He is doing ok or well in Manchester, but the Bee Network, it's not the same as PM.
He won't have the time: because he won't, next GE must happen before Aug 28, it's 3 years at the very best. It s not long to change things (provided you even know what you want to do and no one else is obstructing), and even less time to see whether it works or not.
He won't be able to quell dissensions: he doesn't have the time, authority or character to put an end to internal battles one way or the other. And you know that joke about a Blairite, a Brownite, a Milibandite, a Starmerite, an insider and an outsider walk into a bar...
He has no program or values: he has a history of contradictory statements, he has been mulling over replacing Starmer for months, yet we still don't really know what he would do once in power that would be so different.
Because he is still trying to find it out himself frantically as we speak I bet, surrounded by advisors and communicators, and I am convinced that their only priority is to look good on media and not p*ss off anyone within Labour that could help him in a leadership contest.
Not expecting it's the way to go to finally address the core issues the country faces.
And he is still a Cambridge-educated career politician, who has known nothing but Westminster and the Labour apparatus.