I'm still missing some key point here. Closing the fight means giving the opponent a moment to counterreact, but doesn't mean an automatic lose, not in real-life, and not in fantasy narrative AFAICT.
Closing to melee gives the opponent the first attack. Against an opponent of equal skill, that means you'll almost certainly lose. The orcs will have grown up fighting opponents of equal skill (other orcs), so they'll know this.
In my example, the orcs only have a few spears. The orcs are superior at melee. Just like any historical battle where a foot solider charges to engage in melee, hoping not to be hit by an arrow on the way, the orcs will do the same in this example scenario.
If the orcs don't have their own ranged attacks, they lose. If they stay where they are, the ranged attacks will pick them off. If they move to melee, their opponents get the first strike and so will kill them. The only sane course of action for the orcs is to retreat.
We don't know how miniatures and initiative will factor into a single action round and a 5E with a supposed complexity dial, so I'm keeping an open mind that everything will be synchronized, that's not just 3E or 4E as is with attack or move.
That is true.
That's not necessarily true. It all depends on the details.
Assuming that the two sides begin 30' apart (or whatever the maximum one round movement is in this [hypothetical] combat system) with weapons drawn, it's true that the ranged attackers do get the first attack.
But then the melee closes with the archers and the archers potentially have to "waste" an action to draw their melee weapons, making it even as melee can attack on the second round while the archers can't. Given the reasonable assumption that ranged attacks in melee are either heavily penalized or outright forbidden, it's a draw. The archers can't exactly take a shift every round and still make an attack in this system, after all.
The example postulated that some PCs used their ranged attacks, while others with melee weapons formed a defensive line. It's not an either/or proposition.
The party would still
have melee combatants - they just wouldn't get to do anything.
I would also be extremely surprised if "draw a weapon" didn't become a free action under this system - spending an entire round doing nothing else is going to
really suck even if a round is only a couple of minutes long.
Edit to add:
Combat starts. Round one:
Fighter: "I draw my sword!"
Wizard: "I cast fireball!"
Round two:
Fighter: "I move to attack!"
Wizard: "I cast
creeping obligation of doom!"
Round three:
Fighter: "I attack!"
DM: "Actually, that orc died last round."
Fighter: "Okay, I move over to attack the next one!"
Wizard: "I blast him with a
magic missile!"
DM: "Okay, that orc is dead."
Fighter: "Noooo!"
Wizard: "That's okay, maybe you'll get to attack next combat. After all,
fireball is a daily, so I not kill them all..."