For me, whilst both of these are important points, neither of them are the main reason I prefer switches to pots when mastering. The main reason is fast working. When you have limited choices, you just pick the one that works, fast. No second guessing. It’s far easier to hear/think, “Right, this is the best choice of the 11 or 22 positions I have” and move on, than with a pot where you can easily get stuck in an infinitely descending second guess loop of too much choice whilst twiddling… It’s why I love the TDR plugins too, I have them all in switched/stepped mode. I work much faster this way. If you have a few albums to master in a week, it becomes the primary consideration.
Reproducibility is great for recalls, but the longer I do it, the less of those I get. Was maybe more of a consideration for me a decade ago.
Matched stereo is for sure important. I have some gear that is not switched and it is a pain running pink noise test signals through the chain with an analyser at the end, every time, to make sure the matching is within a fraction of a dB across the frequency range, but I still do it.
Thinking of sending one of my EQs back to the maker to have them swap out the pots for matched Elma switches, I think it would be worth it for me. I like things to be as equal as possible in stereo, but there is also room for the fact that slight variances L to R can make for a larger and more interesting stereo image, and I do know a few people who deliberately set the L and R EQ differently, for example, for that exact reason (although I don’t do it myself?.
That is the very definition of mastering, for me, rather than the “two buss processing” it has seemingly come to mean on the internet over the last few years. Many can make a single track sound louder and better with a variety of techniques, but ensuring good translation on a wide variety of systems, and balancing an entire album timbrally, dynamically, and with the correct spacings, to enhance the emotional impact the artist intended, is an art form where the 10,000 hours rule applies, IMHO.
Mastering is a totally different mindset and technique from recording and mixing. I record and mix one or two tracks a year, but I’m mastering most weekdays the last decade.
As for mono, I recommend you start experimenting with stereo again, it’s a wonderful sounding array that has stood the test of time, and can sound incredible in a nice room with a good system. There’s very little to be done at the mastering stage, in making a mono track sound more stereo, without it completely falling to pieces. I’ve done the “stereo shuffling” EQ technique on mono masters for various clients in the past, and they have consistently said “Nah, we’ll stick with mono”. There’s that, or just slapping some stereo reverb on, but I’d recommend thinking in stereo from the outset if you want to achieve a nice stereo master. Maybe worth reading up on the L-C-R technique, how things were done in the early 60s etc., and trying to implement it in your own works, for an easy starter.