Yep, that’s a fitting term. You definitely still have to rely on macOS (and keep a copy of it around, e.g. for firmware upgrades, which of course basically only come bundled with macOS versions), but other than that, you can do more or less what you want to – as long as you’re outside of it.
I quite like this idea though if I’m being honest, normie users get all the hardened security from the regular boot chain without experiencing basically any difference/downsides, while hardware enthusiasts and (Linux) tinkerers still have options open (well, options that you can get if you have a new chip on a rarer architecture with previously no third party OS).