I agree that GWR's class 800 seats are equally dreadful.
I regularly travel between west Wales and the home counties, and in the days of HSTs and initially the cl800s, I almost always did so by train. It was preferable to four hours on the M4, or five to six hours on the pleasanter but slower A40. But after some very uncomfortable trips - not just from the collapsed seat bases, but also from the occasional violent lateral shaking - I've switched to taking the car every time instead. That has comfortable seats, and it doesn't try to throw me off them sideways every now and then either. It means I can't read while in transit, but on the plus side, I can listen to my choice of music from decent speakers rather than someone else's choice on a horribly tinny mobile phone.
But it's the seats that are the real bugbear for me, and it doesn't seem that DfT, or GWR/LNER, or Agility, or Hitachi, are willing to sort them out. Presumably we're lumbered with the existing rubbish until everyone votes with their feet (or wallet) and switches to cars or NatEx or Flixbus?