Really cannot comment from experience, although perhaps the triple seating plan does seem strange.
I would have thought this would be more for suburban routes, certainly not comfortable for a 90 minute journey.
Mind you commuters from Portsmouth to London have the choice of 2 routes, if I remember correctly (via Guildford via Basingstoke). Do they use the same stock on both routes ?
Both routes use both types, but no-one from Portsmouth would use the Basingstoke route all the way to Waterloo, it probably only starts to fill up with pax for Waterloo at Fareham. There is a lot of interworking of
EMU▸ stock between various routes out of Waterloo, only the Weymouth trains are almost guaranteed to be 444s (yes there are a couple of 450s make it to Weymouth). A few months back I checked a whole day's departures from the 'Portsmouth area', including those that started at Havant, and it is about 50% each 444/450 across the weekday.
Interestingly the 350/2s used by
LM▸ are practically identical (with the addition of small tables for cups in the bay seating) - and they run through services from Euston to Crewe.
450s have also run to Southampton on semi fasts since their introduction, (now extended to Poole) without people spending four years moaning about it...
Paul