I could list the problems with the HD door, but let's cut to the chase and say: It was crap. Total and utter crap.
I have suffered through this situation also. For decades now, big millwork shops use machines that nearly automate the process of building a pre-hung door. You load a "leg" of the door jamb, and the door blank in, and the hinges are automatically routed, and installed. Now, if you have a total F-up of a machine operator, or management that couldn't care, You can end up with nearly useless prehung doors. Unfortunately, the problem isn't limited to the big box stores. When I order trim packages for new homes, I specifically instruct my local supplier that they cannot order my doors from one nearby millwork house, since they are clowns that couldn't care what they assemble. When you are only buying one or two at a time, I would take the time to open them up in the store, and see if they are done correctly. Do the hinges fit well? Are the stops installed neatly, is the lockset bore well done, and in the right location? The one thing I absolutely avoid is door jambs on interior doors that have molded in stops. These are made with the jamb and stop as one piece. The stop cannot be pried loose and readjusted. For older homes with out of square opening, this step can be critical.
The parallelogram was part of what I was worried about in my advice (and I really don't have experience with non-prehung doors.)
It can be an issue, but it's just a matter of using the existing door as a pattern to cut the new one. Lay the old one on top, trace the top and/or bottom edge on the new door and cut.
I was also worried that one 32 inch door might be 1/4 or 1/8 inches off of another even if it was square... and the old door jamb might not be an exact fit.
This I never encountered. Or to be more specific, it is unlikely that you would have a door at home that is larger that the new blank. Having to plane an edge, or taper an edge to match an existing opening, is however, pretty typical.
I understand why a prehung might be a lot more desirable for many, but it's important to see the whole picture. If you are talking about a 1970s unremarkable tract house, and the jamb, or trim need replacement, a prehung can be the way to go. If you are dealing with a nice 1920s craftsman cottage, a new prehung can be a disaster. Not only would you need to disturb old, and occasionally unreplaceable trim, but there is a good chance that the wall thickness or rough opening could be different from modern standards. When you start having to order custom sizes and wall thicknesses, it can get ugly. When I was in the business, a lot of the doors we did were six panel pine, and were used to upgrade newer homes. Often the house was in good shape, with nice trim and perfectly functional, but ugly Luan or Birch doors. Replacing doors was a fairly easy, and cost effective move. Tearing existing trim and prehungs out would of been expensive, and made little sense.