Having used a 221 and a 745 on the same day the difference is quite clear, you can see it.I just struggle to see how a Voyager can be wasting more space than an equal length train that needs power packs (and those aren’t the only non-passenger lengths on Flirts), unless the Voyager was built to stricter crumple lengths for 125mph.
If it’s comparing 2x5 v 1x10 (equivalent) then that’s a different story (which I don’t believe would get funded as it presumably means buying more 10s than half the number of 5s voyagers)
your x12 Flirt is also 10m longer, biasing the stats a bit. Would that fit all the way to the ends of XC?
The every toilet is an accessible toilet and the then standards of crumple zone design leading to massive vestibules on a voyager is part of it,
I assume there's some more space 'lost' by putting tilt mechanisms(or the space for them) underneath means more equipment is needed upstairs, along with the two to three decades more of experience in multiple unit design and technological advancements making components smaller.