HS2 never had to be some kind of souped up bullet train service. All HS2 had to be was an increase in capacity, with any added speed as a bonus. Four track instead of two track - so that fast trains didn’t get stuck behind stopping services. That’s all that was needed.
The speed isn’t what makes it expensive, and it actually does make sense. If you look at the original Y layout vs the existing mainlines, the East Coast Mainline is more direct to Leeds than HS2, so it needs to be faster to match that travel time. Faster travel times also induces travel which has various economical and societal benefits. It will also help to shift more travel from other modes.
The speed isn’t what makes it expensive, and it actually does make sense. If you look at the original Y layout vs the existing mainlines, the East Coast Mainline is more direct to Leeds than HS2, so it needs to be faster to match that travel time. Faster travel times also induces travel which has various economical and societal benefits. It will also help to shift more travel from other modes.