You’re probably right. The stock feeds in these devices pull fr GL repos, not OWRT, so anything that was broken at that snapshot would have carried over. I don’t think even switching feeds to direct OWRT will do it; IIRC OWRT doesn’t backport.
You’re demonstrating you’re not exactly a typical soho user. If you’re still in a return period window I’d see about exchanging the Opal for a Slate Plus. At least you’ll have a far better chance at mainline OWRT. It’s just not going to be worth the aggravation in the long run given your goals. Highly related: