I'm A Banana
Potassium-Rich
I think you forget the "using this material means that, as a condition of use, you agree to/not to...." model.
But you can use the material (the mechanics) without agreeing to jack, because the mechanics cannot be protected as WotC-exclusive stuff.
"Using this material" actually means using the WotC-penned expression of those mechanics.
If you don't touch that with a 10-foot pole (creating your own expression), you're pretty golden as far as the law so far has seemed concerned.