Sorry, I just think this is flat-out wrong. What's the point of having rules at all if it's all completely subject to the whims of a DM?
They're a starting point for when the DM isn't having any whims. Seriously, though, the idea is that the DM will make rulings to make the game he's running better, not just on a whim. As playing games go, DMing is fairly responsible.
DMs are empowered to make adjustments so things work for their games, they are not empowered to just casually rewrite the combat mechanics.
Rulings aren't re-writing rules, just interpreting or overruling them. But, yes, DM's are empowerd to re-write the rules if they want to. Or, rather, nothing can stop them. The assumption in 5e is rulings, though, not re-writes.
So, the idea that it's okay for Wizards of the Coast to publish imbalanced rules just because they provide the caveat that a "DM can change it" (which has always been the case) is laughable in its absurdity.
They can publish an imbalanced system for no reason whatsoever. Or 'because our surveys indicate D&D fans hate balance' or whatever.
Now, it would be absurd if they'd published 5e and claimed it was balanced and the DM shouldn't need to change it, then resorted Oberoni when confronted with the fact it wasn't. But they've done neither.
Keep in mind that originally in D&D you gained experience for treasure acquired not monsters slain.
Not in any published ruleset. Indeed, one of the changes made by the first supplement to OD&D, Greyhawk, was to reduce the exp for killing monsters.
Which again, assumes the rules are imbalanced.
Of course they are. And not just on the tautological grounds that perfect balance is impossible. The question isn't are they balanced or are they broken, but whether that can be excused because the DM is Empowered to enforce spotlight balance and assure playability, or whether Oberoni applies. Key reasons I have to argue it's the former are that there was no particular call for or prioritization of balance leading up to Next or during the playtest (in fact, plenty of the opposite), and that the explanation of play includes DM rulings as a matter of course.
The thing about Oberoni is it's not talking about rulings, but house-rules. There's a distinction. House rules replace/change existing rules. The result is a different ruleset. Ruling don't replace rules, they might override the results of a rule, or cover a situation there's no rule for, but they don't change the rule itself. When a rule is broken and the DM changes it, the rule was still broken, even when an off-hand 'Rule 0' says "BTW, change any rules you want." When the rules say "and now the DM makes a ruling," the DM isn't changing them by making that ruling, he's just working with them.
The Oberoni fallacy still carries plenty of weight.
Only to the degree the game purports to be balanced in the first place. 5e rests so much on DM rulings that it doesn't need much, if any, mechanical balance to be playable. You want to complain that 5e isn't balanced, go ahead. It isn't.
WotC carries a responsibility to strive for a well-balanced ruleset.
Nope. They're selling a product, and how well it's sold has been darn near inversely proportional to how well it's been balanced.