I don't think he was ever intended to be PM. He was brought in to make the LP electable, which I think he is doing well. He is an excellent contrast to 'Boris', and comes across as professional and competent, which is more than can be said for the PM.
It is interesting that people always refer to him by his full name, or as 'Starmer', whilst using the PM's 'stage name' of Boris. To me this indicates the differential in the amount of respect in which the two men are held.
In the end, though, I think that a more charismatic candidate will be in place before the next election. Unfortunately, the public is now used to soundbites and entertainment instead of debate and statesmanship, so someone like Sir Kier will struggle to compete for attention. I wonder whether Andy Burnham will be a good alternative? He is personable, sensible and is good in front of a camera.
I agree that the Speaker is hopeless, and that this is why Johnson gets away with so many lies. Love him or loathe him, Bercow would never have allowed it, and whatever their politics, I'd like to think that most people would see this as a good thing.