William-- the point isn't what you prefer or even what the default is now. In fact column view was the default when Apple Mail first launched many years ago if you want to make that argument.
The point is that lots of people still prefer columns but they have been dumbed down significantly to function in a non-standard, way from all other Apple folder and finder windows. Namely there is NO flexibility to choose which columns, or widths or order etc. On a big monitor, less of an issue. On a laptop, a big issue, almost unusable.
BTW, I was the one who started this thread. To summarize, I have been an Apple user since the 1980s. Am (actually was) a software developer and understand what it takes to code things like this- would doubtfully be hard to implement since standard objects already being used in the OS that could be re-used here.
I have tried all the other email alternatives out there suggested on this thread. The best is Thunderbird, although not without some silly, unnecessary constraints also. About equal in tradeoffs for Apple Mail at the end of the day in my opinion. Thunderbird got purchased recently, so I am hoping the new company will make it sing.