See, you use all this thinking, but everyone knows there's absolutely no difference whatsoever about life under the Blair/Brown/Starmer governments and that under a potential Führage government because neither Blair, Brown or Starmer conform to the resolutions of a 17th International, held in a phone box in Neasdon on a Thursday night in February 1983.
/PetulantUrbanTeenager mode off.
My considered view is that you're right, that eventually a far right, Trumpian/Führagist Tory party will emerge as the government - and it's going to be shit. Unrelenting, diabolical shit. But that by voting Labour, by knocking on doors, by getting involved, you push that government further off into the future - that it's far better to live for 5, or 10, or 15 years under a frankly uninspiring Starmerite government, and then 5/10/15/forever under a Trumpian/Führagist authoritarian, dystopian nightmare, than it is by just accepting that Trumpian/Führagist hellscape right now because Starmer isn't going to nationalise the railways on day 4.
Successful politics is the realisation that you can either have some of what you want, some that you aren't happy with, and a bit of what you really don't like, or you can have none of what you want, and a lot of what you really can't live with - and that one of those is very much better than the other.