I think there's two things you're forgetting:
- Comparing a Pendolino to an 80x the acceleration isn't even close. You're going to regain a lot of time through the far shorter time taken to reach full speed. (With that in mind if I was in charge of the diagramming I would have the 80x allocated to routes with the most stops to gain maximum benefit from this but I am sure there are other concerns which I've not noticed)
- There are other sacrifices to be made in implementing tilt. As well as the cost, the Pendolinos and Voyagers have unusually tapered bodysides and high floors which gives them an unpleasant cramped feel. For all their flaws, the 80x interiors are actually very spacious and if it comes at the expense of a few extra minutes of travel time then I'm sure many, myself included, will be happy with that sacrifice.
I don't think tilt is as revolutionary as is often made out. If it had actually got large parts of the WCML up to 140 then maybe I'd have more faith in it, but honestly I think WCML tilt will just be another entry in a long list of failed technological endeavours on the railway.
Of course that doesn't mean there's no place for tilting trains, but I don't think they are massively significant in the UK so far.