I strongly doubt the overwhelming majority of consumers are going to cross reference booking details against an external site to avoid a specific plane unless there are planes falling out of the air on a daily basis. People may say they will, but in practice they'll look up the cheapest flight and book that, as usual.

Depends on how prominently the information is displayed, and the price difference.

If I can see the plane type in the list of available flights, and the difference is $15 on a $250 ticket I would choose the non Max flight, all else being equal.

Fair, and someone mentioned that Kayak does display that, but I think you will probably have to move to a different airline to get a different aircraft type (airlines use one common type for most flights on a given route) and the price differences are often steep and/or there are other sacrifices to be made (frequent flyer miles, more expensive bag checkins, etc).

I don't disagree at all. The information's there, though.