You can't argue that to get around vague and unclear rules you should "Just use common sense".
D&D is not a game about common sense. Many core mechanics defy common sense.
I agree. Common sense is a bad way to do things as it will vary from table to table. I do think 5E is fine varying from table to table. I think it expects to vary from table to table. The only group that needs a consistent set of rules is Adventurer's League. I don't know about you but after dealing with the rules being tailored to fit
Pathfinder Society, I don't want rules that are consistent based on
Adventurer's League or whatever organized play group D&D works with. Maybe you like
Adventurer's League concerns becoming the primary way for D&D to create consistent rules. I certainly don't want that. Then the rules become that groups version of "common sense."
I get tired of DMs who say "Its my game so you'll do what I tell you!". The DM is a player too, just like everyone else. Some groups are ok with vesting ultimate power in him, others are not ok with that, and the rule book is the contract that each player agrees to abide upon, just like many other games, including the very popular pathfinder.
One of the complaints concerning
Pathfinder is the rule lawyering. DMs don't like that. It makes many DMs quit playing or not enjoy the game. And you're right, the DM is a player. He is the player that has the most work to do. If his players are doing something that completely wrecks the game, he gets to kill that...after a discussion usually. The DM isn't some kind slave to the players that they purchased or even their employee. He's a guy doing work that others often don't want to do to run a game so people can have fun, including himself. He isn't bound by any contract.
They have reached a point where the Pathfinder rules are so convoluted, overly-complicated with so many insanely over-powered combinations that DMs have to excise feats during play because they came out in some supplement they hadn't read creating some disastrous rules combination that destroys any semblance of game balance. Then when they do that, players that want to act like rule lawyers try to argue with them creating a tense, argumentative, and unpleasant environment.
5e is clearly aimed more at the former group than the later group, with the "story" having emphasis, milestone leveling being encouraged, and vague rulings not rules philosophy. That's ok, and I understand the design intent.
It doesn't mean however that some rules couldn't do with some clarity, or at least just completely ditch the mechanic aspects of them and go completely DM fiat.
After all the designers did say they will only errata stuff that causes arguments at the table. I'm simply chucking in my observations on things that not only have caused arguments, but where confusing in the beginning, and some (passives) still somewhat arbitrary and confusing today.
That's fine. Stealth doesn't cause arguments at my table. Then again we enjoy pulling out the ruler and thinking about whether someone could see someone at a given positions. Only takes a few seconds at this point. We play a pretty "realistic" style of game where the players don't do stuff like cast a
fog cloud to nullify ranged penalties or hide behind the same box again and again. The rules seem to be clear for players like us that use a naturalistic play-style.
All we needed to know was the following:
1. You can sneak up on someone with a Stealth role as long as they can't see you which we translate as "As long as you're making a reasonable effort to be unseen and unheard, you can stealth."
2. You get advantage on the first attack against attacker when you attack from surprise or aren't seen. Once you attack they know your location and you no longer gain advantage.
3. Cunning Action: Hide: The rogue can move and hide on the run. If the target can't reasonably discern where the rogue is like in a forest or a warehouse with a bunch of boxes or in forest mist for a wood elf or a melee combat with a bunch of people for a halfing, the rogue can gain advantage for being unseen on his first attack throughout a combat.
4. If the target can see the rogue whether through process of elimination such as watching the only corner in a room the rogue is hiding behind or a single box, then the rogue doesn't get advantage and is seen.
We determined all this from reading the rules text. The entirety of it. Not just the pure mechanical stuff. But the examples in different areas of the book such as the Halfing and wood elf special ability. Unseen attackers. Blinded condition. Hiding. It all adds up to an easy adjudication of the above.
About the only thing they could add as errata to make the people that seem to need things made clearer is a sentence that says "The DM makes the final decision whether Stealth is possible in a given environment or situation." Add that sentence under Stealth for those that need it, WotC's errata problem with Stealth is solved.