I think ME3 pretty much forgets about the whole Relay traverse thing. It's odd that it never gets brought up when Shepard speaks of the Quarians retreating and there are other instances in the game where that kind of stuff happens (like the Victory Fleet). Why I bring this up is because if the writers never considered the limits of Relay travel when writing the Rannoch bit it could have been very possible for the Quarians to in fact retreat because that limit seems to have dissolved for the purpose of the post-Dreadnought scene.
See, inconsistencies like this are why debates like this never die. Rule of Cool trumped internal consistency, making definitive arguments harder to make. The Thanix Cannon, we are told, operates by accelerating liquid metal to relativistic speeds... until they want a scene with a Reaper being destroyed by rockets, so they pull "Thanix Missiles" out of their butts. Never mind that the two concepts are wholly incompatible; "our Thanix Missiles do a f***load of damage," don't think about it, just nod and find something else to shoot. Same thing for the Cain firing a projectile that homes in on its target like a moth circling a lamp instead of moving in a linear trajectory like any other mass accelerator slug. Same thing with Bekenstein being accessible via FTL from the Citadel when ME1's codex established that the abrasive qualities of the Serpent Nebula made FTL in its vicinity impossible. Same thing here.
The argument I make is only valid if I stay consistent with the rules the writers established, even when the writers don't. Nothing I do can change that. It comes down to how others choose to see the situation; if they're OK with the lore turning inside-out to enable it, they won't accept any argument that evacuation was impossible.
(To put things in perspective, moving 50,000 ships through a relay, one ship
every second, non-stop, would take just under 14 hours. Does anyone expect a ship filled with hostile, Reaper-controlled Geth to
stay disabled for 14 hours? They already have the Reaper signal back online just in the time it takes to get back to the Normandy. There's a reason my IdiotShep was the only one to suggest a retreat.)
Withdrawing your civilians with support fire from your Patrol fleet and having the Heavy fleet watch the Geth withdraw. That said, the actual plan, right up until the 'FRAGO' by Gerrel was to use the opportunity from disabling the Dreadnought to retreat. That was the stated intent in the game. I'll see what you have later.
See the above, and also note that separating the civilians from the military fleet both leaves them unprotected
and cuts off the military fleet from its entire supply chain (Xen: "Even Koris recognized the value of the civilian fleet. The invasion would be stalled without a supply chain, after all").
The fleet cannot divide itself because it's wholly interdependent. Out of 50,000 ships, only a few hundred are actually dedicated military vessels (the Heavy and Patrol fleets). The civilian fleet relies on the military for protection and coordination, and the military depends on the civilians for food, fuel, etc. According to ME2's secondary codex entry on liveships, each ship in the fleet is dependent on
daily deliveries of food, so your military would quickly run into trouble without one. Hold back a liveship to stay with the military fleet, and you'd be forced to keep 1/3rd of the civilian fleet (roughly 16,700 vessels) in the Tikkun system with them to keep
them fed, while leaving two-thirds of the fleet drifting without protection (unless you want to divide your military forces further).
As for why destroying the ship was the right move, even after Legion (or the VI) shuts down the drive core and is disconnected from broadcasting the Reaper signal, every Geth on the ship is still shooting at you, signifying that those on the dreadnought remain under Reaper control. They'd try to reactivate the core as quickly as possible (they're flooding in to attack you seconds after shutting it down), and with that would come barriers, engines, and weapons. It would have been a different situation if the Geth on board actually
ceased hostile activity after the signal was disconnected, but they don't (incidentally, this is why I think the "good faith gesture" thing was bullshit, one of multiple instances in the arc where they bash you over the skull with Geth Good/Quarians Bad - what we're told doesn't mesh with what's actually happening around us). When the core came back online, Shepard and company would once again be trapped on the ship (if they had not yet evacuated), or sealed out (if they had), and the dreadnought would go right back to tearing into your only allies in the system unopposed. The only unknown was how long that would take.
I won't defend Gerrel cutting off communication (even Shepards who agree he did the right thing call him out for doing that), but destroying the ship was the right move. Hackett didn't know how long it would take before Sovereign's barriers, engines, and weapons would come back up either. He blew it up right on top of Shepard, in the Council Chambers. I don't see anyone expressing the wish to assault him for it.
Gerrell has an itchy trigger finger. He would've shot at the dreadnought even if his mother or child was onboard. Instead of punching him I would've shot him
Great. Who do you put in charge of the Heavy Fleet, then? Who's the substitute?
Here's the Migrant Fleet's ME3 map description:
A flotilla of 50,000 craft holding over 17 million quarians, the Migrant Fleet is the largest array of spacefaring vessels in the known galaxy. It is a testament to the quarians' strategic skill that these numbers have not dropped significantly during recent battles. The fleet is now on the far side of the star from Rannoch, the better to cloak its movement from the geth.
That's with Gerrel in charge of military maneuvers. Side with Raan over Gerrel, and the heavy fleet gets ripped up. Raan is basically the police commissioner - she doesn't know how to fight a war. Xen is a scientist. Tali is a computer expert (who is keenly aware she isn't a real admiral), and Koris is an (elected?) civilian. Like him or not, Gerrel is the one out of that bunch who knows what he's doing. Hackett, by comparison, lost an entire fleet to allow two others to escape. In light of that, Gerrel arguably did a better job keeping his people alive (unless, of course, Shepard stabs them in the back later on, but that's another essay). You can charge him with whatever you want after the war (along with the Asari Matriarchs, and Shepard himself on account of Bahak). But killing him, putting someone else in charge while the Geth remain under Reaper control... Shepard's little tantrum is going to get a lot of people needlessly killed.
EDIT: This is gonna turn into a Battle of the (Off-Topic) Walls of Text, I just know it...