That mindset has made flying in the US the experience it is today.
Your comment rings sanctimonious to me.
While I agree that major airlines should do better in some areas, they are also just responding to consumer demand.
Should the people who cannot afford higher fares just exist in a lower caste where flying is not achievable? Those people for whom lower fares are the priority, you feel they just shouldn’t be able to attend a family member’s funeral or college graduation?
That is how things are in my extended family in the US. A spare couple hundred dollars for even a routine round-trip fair between major cities is still a very difficult stretch for them.
If grumpy people who can easily afford the flights are annoyed by the lack of frills and the cheapness, yet people who are less well off can possibly afford more flights, that seems like a positive overall for society to me.
Unfortunately in the airline industry we've tended toward an overall race to the bottom which explicitly budget airlines and different classes of service only help to a limited degree to separate out people with different preferences.
What it sounds like you are saying is that there is a group of middle class or upper middle class people who won’t choose to spend the amounts required for the luxury option (the equivalent of not taking the bus), and yet feel grumpy that the slightly higher prices they would prefer to pay end up pricing almost all flights out of the market for other middle class or lower middle class travelers.
“Cleanly separate the cheap vs comfortable use cases” seems simple: airline economics just implies that the prices for the comfortable (“not taking the bus”) option are staggeringly high, and that so many customers strongly prefer the cheap (“just treat the airplane like it’s the subway”) option, that airlines must structure the offerings around that fact.
That said, if you have Pre-check, airline status, airline club membership, maybe pay a bit more, etc. in practice you get a bit more legroom, early boarding, (usually) fairly fast security, etc. So, in that sense, there is a mild upgrade option relative to barebones cheapest tickets. (Depending on the airline.)