Earlier quoted context omitted.
Sure, but the outrage from this change came about revoking the license for past works. By putting SRD 5.1 under CC, the situation for many indie creators of working with the SRD becomes clean and clear. Hasbro can do whatever they want going forward with D&D.
Game rules/mechanics usually can't be copyrighted other than just the literal text of descriptions of them. Does this give anything you couldn't have by cloning the rules with different wording flair?
What D&D editions do is develop a set of base mechanics, basic probability distributions, and then create a framework on how to apply them. This includes monsters, races, and classes which have particular attributes or play feel. This includes common roleplaying conflicts and guidance on how to adjudicate them. What a lot of indie RPGs that used OGL 1.0/a did is they made references to things from D&D and used them in ways inspired by D&D. Think "elves" or "faeries" being associated with the mechanics and tropes you'd expect. Now with the new CC-BY-SA 5.1 SRD, you can make explicit references to Elves in derivative works and also license it under CC-BY-SA.
There were always completely separate systems that borrowed nothing from the play feel/world of D&D. Those communities/creators had nothing to fear.