Surely the simple truths are that: the Tories have no hope of winning the next GE; the best they can do now is damage limitation; Labour’s majority will be so big that they will get two terms at least; over that time Labour will face all the problems confronting the UK and world economy now; people will come to see that Labour have no better prospects of improving life in the UK than any other party.
Two issues in particular will be difficult for Labour. One is their supporters’ (or most supporters’) clamour for re-joining or effectively re-joining the EU. That is politically very difficult to manage. The other is unplanned immigration. No government can do anything about that and - rightly or wrongly - it does damage any hapless looking government, as we see today.
Stale government will nearly always lose.
On personalities, I suspect Starmer will end up like Major. A decent man, underestimated, but very dull, and the effect of ridicule will corrode his leadership.