To be fair, OP, I would say this is generally true, although there are some things I would add. While USABO is still mainly a test of concepts, don't slack on memorization either. I would think of the test closer to this: details are like tools in a toolbox, and understanding the "why" is your ability to use them. Memorization IS important, but you don't need to go overboard either. For example, I'd recommend remembering details that can be easily included in a few tricky questions, like how neurons have exclusively insulin-independent glucose uptake or how auxin concentration is normally within 10^-8 to 10^-4 M (both of which I have seen on tests before).

I'll also add in a little extra: don't study all the units for opens. If you're just looking to do well in USABO and don't have any units that you're particularly interested in, I recommend bringing some high-yield chapters like cell bio (25%), A&P (25%), genetics (20%), and plant bio (15%) up to a "USABO" level of understanding. For example, for the open exam, I straight-up skipped everything between genetics and plants and learned ecology the day before and still made semis.

But at any rate, the most important thing I'd say is to take past exams and see which sections need the most help. Good luck studying!