At your table the rules can deviate as much as your group wishes.
The license is for the Forgotten Realms.
Isn't the license also for the non-SRD rules? Most of the subclasses, all the feats except for Grappler, etc? E.g., the only Fighter SRD subclass is Champion, so the license allows Larian to use Battlemaster. This is especially relevant since Larian wants to give the players options, and Champion Fighter is the complete opposite of this...
It is and it isn't. Mechanics like subclasses and feats and such are in a very grey area, legal-wise. I don't think there's a lot WotC could do if somebody were to recreate the Eldritch Knight subclass or the Lucky feat, for example. But the IPs and trademarks are much more legally "tangible" if you get what I mean. They're defensible and easily recognisable. They're big selling points.
Makes sense. I imagine it strongly depends on the amount copied. If someone recreated a Eldritch Knight without D&D 5e license and called it a "Mage Knight", WotC probably couldn't do that much about it. But if someone recreated ~all of the 5e subclasses and feats, then WotC would have a good copyright infringement argument even if all the names were changed.