I could be wrong, but I'm under the impression that whether a plane is cramped or not is largely up to the airline not the manufacturer, since it's the airline who actually makes the decision about how many seats to cram in, and what sort of seats to use.

To an extent, but the airline interior layout is constrained by the fuselage diameter. The A320 is somewhere between 6" and 12" wider in usable interior diameter. For a similar layout (3 and 3), you can have marginally wider seats in the Airbus, or slight more aisle space, or a bit of both. And, in theory, the larger fuselage also allows a bit more overhead space.

Newer planes also tend to have better environmental controls (air pressure, lighting, etc).

It’s not just that pilots didn’t need new training, because they were still supposed to have some minimal training on the changes.

Pilots can only hold one type certification at a time, and have to retrain to switch between them. Southwest pretty much only flies 737’s and is heavily interested in the MAX because it means they don’t lose the ability for pilots to fly their other aircraft due to retaining the same type certification.

Pilots can hold more than one type certification, but they have to keep them current. There are many pilots who fly more than one type of aircraft routinely.

Boeing tried so hard to avoid "retraining". Yet the training isn't that expensive. It's about $22,000 for an airline pilot to move from another aircraft to a 737 family aircraft. Takes about a month. And that's like an Airbus to a Boeing switch, not just between similar models. If Boeing threw in a few training credits with each aircraft (each costs about $100 million) that would have solved the problem.

> Pilots can only hold one type certification at a time

Source? I am pretty sure pilots could hold any number of type ratings (sic) at any time, but it's uneconomical for the airline to keep them rated (and current), so it's rarely done.

i've read that for pilots, the 737 is better and more manual (if the need arises to fix things or do overrides) compared to the airbus a320 which is a bit newer and has more electronics and sort of does a lot of things for you, but also obv more likely where things can go wrong

Airbus planes have had their own share of problems, including really basic sensor issues (Qantas 72 for example), but they have started doing fly by wire more than 30 years ago and by now they are solved.

Airbus and Boeing have had very different perspectives on flight automation, with airbus tending more towards computer control. I’m not a pilot, but I’m given to understanding that Boeing is slowly shifting over towards Airbus’ style, with more computer intervention in pilot actions.

But they're SAFE and reliable. Their track record in the air is pretty amazing.