delericho
Legend
I would say the Holmes estate can't claim copyright over retirement, either, but they sued over it. Can people use the distinctive plot elements unique to the 5E Monster Manual versions of OGL creatures? I'm not nearly so calm as you that they can't claim ownership over them.
It's worth noting that the articles says that they've sued claiming ownership but doesn't give any indication of whether they won or not. And it's further worth noting, then, that WotC could sue someone for using the Ettercap/fey war even if they have no legal grounds to do so and even if that third party had checked with a lawyer that it's okay - BobTheLawyer saying "you're okay" doesn't guarantee that WotC won't claim otherwise. (And, indeed, until precedent is set, all BobTheLawyer can offer is his informed opinion. There's no precedent as regards the OGL.)
Checking with a lawyer can provide some measure of confidence, but it can't provide any guarantees (at least as far as the OGL is concerned).