I laughed at the Toyota test, because there's a ton of truth in there. Got to test the mix on bad speakers to see if it translates...humbling, but necessary for a good mix. I do test in my car (coincidentally, it is a Corolla) as well :)
It's definitely sage advice!
† edit: Looks like I fell victim to hearsay. It's just something I'd heard so many times for so many years I assumed it was true, and it may be partly, but here's a great write up on the subject—tangential to the main thread: https://www.soundonsound.com/reviews/yamaha-ns10-story
I have a few rock CDs from the 90s (Dizzy up the Girl is one) that ar completely unlistenable in many cars; too bad Petty wasn't involved in mastering those.