Doors in the middle, I don't mind, it makes boarding and alighting quicker, I wouldn't object to the 390's having the same door positioning... (Yes, I know it'll never happen)
Since the 350s were increased to 110mph, they've proven credible alternatives to 390s, except for uncomfortable seats. Cold air aside (which ironically seems to what you want), the 350s easily win on ease of access. Like any train though, the 350s do vary. I've been on a fair few that feel/smell like the air con is broken. But then you can usually switch carriage.
There are obviously several overlapping categories of passenger: reserved/not reserved, able/less able, with/without luggage, commuters/not commuters, kids/no kids. 390s seem to suck at everything the less able, luggage bearing, non-commuters with children need. They incur "boarding" and "disembarkation" overhead (also known as passenger stress) at major stations, which just makes the hot and cramped feeling worse.
I wonder if some of these view points have fed into (aside from cheaper walk-up tickets?) the sheer number of long-distance travellers that we see on LNR commuter services? (pre-COVID, this was a often a problem for LNR users south of Rugby)
Add to this the need to book seats on Avanti for cheaper tickets, and you can end up somewhere awful. I used to dread being booked into Coach A as it only had a single end, and if the train was busy it felt like you were trapped for three hours.
Could be worse, you might have to endure 158s at rush hour...
