It is utterly ridiculous. That a person couldn’t or wouldn’t call ahead when they were such a distance away as the OP stated and simply prebook a double slot is beyond ridiculous. It’s not 2013 nor 2018 nor are either of those models new to the market, though one is still in a high demand period which could cause a delay in test driving availability.
And because demo vehicles and advisors can still be a limited resource here’s another thought, one could book a single test drive of the vehicle they’re most leaning toward and come back a month or 6 later and book to test drive the other model.
Or one could book a test drive of one vehicle at one location and book the other vehicle at a different location and simply time such test drives when they’re in the area visiting family, friends or when on vacation, or, or, or. Tesla is not going to stop a person from doing those things.
Obviously, if you just show up there may not be a time slot available or the vehicle you want to test drive available. That happens at dealerships too you know, where at some locations vehicles and salesmen can be a limited resource.
Don’t be a dumb human and not think ahead. Don’t be a dumb, arrogant, entitled human and think you’re somehow special and that anyone is going to drop everything and cater to you because you’re spending some money.
I guarantee I could contact the Tesla location in question and manage to get myself a test drive in both vehicles if they were available by being pleasant, reasonable and understanding. Yes, part of being those things would be to compromise if needs be and maybe not getting the test drives exactly at the times I’d most prefer.
What I don’t do is make my first post on a Tesla enthusiast’s forum about how Tesla won’t let me test drive two vehicles and go on about how much money I’m prepared to spend. That person calls me to book an appointment for anything and instantly my schedule is full from now until you know what freezes over.