I was quite happy travelling on a 455 in the suburbs and was surprised they were going. We were lucky, they were a much nicer experience than a 315 or 313 (honestly, I don't understand the love for a 313).
If the choice was 377s every 30 mins, or a mix of both every 15 like it was, I'm choosing the latter.
In London, I found reliability to have improved with the timetable change before Covid, so I'm not surprised it's still working well with less trains, although it takes some skill to match the demand and not screw it up.
The interiors have certainly improved. The improved screens are welcome and they feel clean - almost every seat had stains on them until recently; either gum, brown or white patches - your mind naturally wondered what it was...
They're also getting busier on weekends, that's probably just summer though. I visited Rye on the weekend, I was surprised at how many people got off a 3 car 171. While from London Bridge, the Victoria service at 7-8 cars was also busy (and contrary to popular belief, toilets are very much used on suburban services).