But the class 345's are for Crossrail - GWR▸ won't be operating them and they also won't get any further west than Reading, so they are probably perfectly fit for purpose as a high capacity outer-suburban commuter train rather than the 387's which are intended for longer distance services, hence the different interior arrangements.
No toilets, outer-suburban?
In my opinion, having no toilets (and/or metro-sliding doors, like the class 150 and class 376) instantly classifies a train as strictly inner-suburban. It is the 387s (plug doors, but wide ones away from the vehicle ends, and toilets) that are outer-suburban in my view (not been on one myself though, so the seating might not be up to the standards I would consider suitable for outer-suburban work).
I was making a comparison to the Metropolitan & District lines S-Stock which have no toilets (and never have had in my memory) and also have a lot of longitudinal seating - they work perfectly fine for journey times which are similar to central London to Reading on Crossrail (45-60 minutes, I suspect journeys longer than this on will be unusual). Crossrail should be viewed as something akin to the Metropolitan and District lines in terms of shifting as many people as possible in a quick & efficient manner - lots of doors and circulation space are required to achieve this. I fully appreciate some users have a greater need for certain facilities but
in my view CrossRail is more of a 'metro' type service rather than a traditional heavy rail service, so it seems logical that facilities are similar to other routes such as the Metropolitan line.
The 387's will (maybe one day...!) be used for longer journeys to Oxford and Bedwyn, so I agree those need a few more creature comforts in terms of toilets and space to allow people to work or whatever on their journey.