I think you have your thoughts well ordered and correct. The single boiler machine will make great espresso, if it had good thermal managment via a PID, rather than the cheaper systems that are sometimes used on some machines. e.g. Shot temps varying by 6-8C , depending on when you pulled the shot if they have no PID, but a more simple thermostat (electronic, or manual). You also have to remember to refill the boiler after steaming. Usually this means opening the steam wand and running the pump.
HX do have compromise over temperature and you won’t ever really know what it is, this is because it depends on the length of your flush, time between shots and boiler temperature you set.
If you want to remove all compromises, then dual boiler is the way to go.