The doors in the driving coaches are at 1/2 and in the intermediates are at 1/4 and 3/4, but because the driving coaches have a smaller passenger cabin the distance between doors is about the same throughout the train. The gangway between coaches is full width so it's easy enough to move to the closest door in the next carriage.
This isn't correct. The passenger cabin on the end vehicles is, like basically all Stadler FLIRT/METRO type modular units, the same length as that of the intermediates. The space taken from the potential second door is on the wider windows (don't just count windows, it's misleading on modern trains as other than on Bombardier products they're almost never all the same size!)
The Stadler modular design makes the end vehicles longer by bolting the cab on the end so the passenger cabin is the same size (generally about 16m).
This photo from Flickr by user Martyn Hilbert illustrates it on the 777:
The new order on Merseyrail.....with 'Not in Service' on the front destination display, four-car Stadler built Class 777 777010 was passing Kenilworth Road to the South of Ainsdale with the 16.22 Southport to Sandhills working (5U06) on July 19th 2021. The unit was undergoing daylight mileage...
www.flickr.com
That photo (which I almost used as an example myself) clearly illustrates that the end vehicles are considerably longer than the intermediates.
And this photo from Wikimedia illustrates how two sets of doors on the 555s leaves little room for actual passenger accommodation:
The Metrocar vehicles are considerably shorter than the Merseyrail ones and the use-cases are a bit different (as the city is much smaller). It was pointed out above that the Merseyrail units aren't technically FLIRTs, but they do seem to have used a lot of the FLIRT derived modular body components to build them, and the same structural principles seem to apply (longer end vehicles due to the cab and the bogies, for instance).
Stadler will of course do you any door layout, so some more thought could have gone in, as it has on the Metrocars, to ensuring the doors are evenly spaced on the bodyside. Unfortunately while a lot of thought did go into the 777's design, most of it appears to have made things a lot worse than just picking a fairly standard Stadler design like the Anglia units.