Yeah but you never know when you'll need to use a 10-30 or 5-20 or 6-20. The whole point of the UMC is to have something that you can use to charge your car in an emergency, which is why I keep the UMC and all of the NEMA adapters in the trunk at all times.
My experience is that I was at the SFO long term parking garage and the garage with the ChargePoints in them was "full", as in the staff wouldn't let me in there. I don't think all of the CPs were full as about half of them were showing up as unused. In any case, I went into the other (older) structure and went to the NEMA 5 outlets, and realized that they were 5-20 instead of 5-15. So I got my 5-20 adapter out and used that one to charge.
Then you've got to at least get the 10-30 and 14-30, because for rental houses or relatives'/friends' houses, if they don't own an EV, they're most likely to have a dryer outlet. And of course, you should have the 6-50 and 14-50 because those are the most common outlets at camping sites and in garages that are equipped for EVs.
And that leaves just the 6-15 and 6-20 out of the mix, but at that point, you might as well buy the entire set.