Vyvyan Basterd
Adventurer
Standing in front of them?
Even pre-grid days it was obvious that a human-sized person could not effectively block a 10-foot wide standard D&D hallway.
We could sit here all day, probably til the end of days, and discuss, "Well, what about this circumstance?" and "Nuh uh, what about that scenario?" But going individual round by separate corner case is not going to get anyone anywhere...and we'd NEVER see a 5e get finished.
The Fighter trying to protect the "squishies" is a corner case?! You just said upthread that the foes are gunning for the Wizard, it would make sense that the front-liner would commonly try to protect him. That's the opposite of a corner case.
I suppose its a playstyle thing, but if there are combatants in front of the mage, I never let the enemies just waltz around them to take a swing at the wizard. If they have missile weapons and want to try to shoot passed the melee folks, that fine. But they can't just race by the fighter for the wizard instead...there's 3 dimensions of armored fury to get by first.
Why can't they? Without passing attacks or opportunity attacks nothing stops them from doing so. Unless you totally disconnect the rules from the reality of the world any mass swarming creature, like orcs, goblins, kobolds are going to figure this out.
And if a DM doesn't force their monsters to stop at the first creature they meet like you do, then the player of the Fighter feels like his role as protector is useless.
There's situation-to-situation circumstances, of course. If it's a large or outdoor area and the party just wandered into an ambush from both of their flanks, then, yeah, obviously the attackers will be able to go straight for whoever they want. But in a "face-to-face" dungeon kind of encounter, there's probably not enough room for them to "just go around/ignore" whoever is in front.
It was common enough in the games we played back then to happen more than once per session.
There can not, nor should attempt to, be rules for every possible permutation/scenario that might/could possibly occur in game. That way leads to confusion, eventual contradiction and almost certain madness.
True. But commonly occurring scenarios shouldn't be left for the individual DM to decide whether his creatures will play nice and not just move past the impotent Fighter.
The rules don't have to, again, nor should say "everyone must apply this level complexity to their game." They need to say, "Here is the bare bones basic simplest framework of the game. Any game of 5e D&D uses this starting framework" and go/add on from there.
OA/AoO are not that "bare bones/simplest possible" mode of playing...with or without the use of grids or miniatures. Hence, optional module. Tack it on when you like...tack it on all of the time...don't tack it on at all. Up to you/your DM/table/group.
I can see your point in this regard even if I don't agree with you.