ThoseDeafMutes
Member
They're not undetectable - their signal just doesn't travel faster than the speed of light, so by the time you see it, they've taken off. There would still be a 'wake' left behind, and any station that happened to be inside of that before they got to the relay would be able to phone ahead and go "Holy shit guys this radiation, something's coming, might wanna lock the door". They'd still be able to spread around pretty damn quick, but there would be enough time for the Citadel to scramble its defense.
Fair, but this requires observation stations in the systems you're passing through (and unless they're pointing a telescope at the exact point you're zipping past they won't see you anyway, but I digress), and most relays aren't even mapped, let alone most systems being occupied. I mentioned attacking from "Above" the galactic plane because this passes through the minimum number of systems - the Milky Way is only 1000 ly thick compared to 10,000 wide. And again, all they have to do is hit the first relay and then zip straight to the citadel for a surprise attack.
The amount of time you get for a warning is "less than a day", at most (probably more like an hour of warning), compared to the weeks Sovereign gave them by tipping the galaxy off, and then the two+ years it gave by failing and getting destroyed. It also doesn't require waiting 1000 years and giving them the time they need to examine the corpse of their fallen reaper bretherin (which will not end well for the reapres, THANIX GUNS HO).
And while 'tons and tons of Reapers' is still probably a losing battle, it might not be so entirely one-sided; remember, Sovereign fucked shit up, but it was Sovereign and a gigantic Geth fleet that did the attack. It's very doubtful that an individual Reaper can fight a proper fleet to a standstill (if they could, why bother with the Rachni and the Geth in the first place?). The Reapers would probably win, but it's quite likely they'd take some pretty heavy losses, which I'm sure they wouldn't be too happy about.
Sovereign didn't even fire a single shot until after it had taken a pounding for more than 15 minutes beccacuse it was attached to the Citadel towever. Even during it's initla charge all it did was ram a ship that was in its way (and probably not because it wanted to destroy it but becacuse it wanted to take the fastest route to the citadel). Sovvy having the geth fleet implies that it didn't feel confident that it could take the fleet itself (or at least it couldn't stand up to their bombardment while it wasn't fighitng back, attached to the tower). However, when it did start firing it was a slaughter, one-shotting the Alliance cruisers etc. EDI in ME2 stated that "Reapers are impervious to dreadnought fire", and while I'm willing to take that a an exaggeration (I don't buy that they can't be harmed by it given the previous inference about Sovereign vs Citadel fleet), it still does mean that a fleet of 200 Reapers would be an untouchable military juggernaut. The citadel fleet only had one known dreadnought to begin with, the Destiny Ascension.
I would be stunned if the reapers even took a single casualty in that sort of battle.
While yes, they technically could have done that at any time, there's no telling what kind of toll it would actually take on them. The energy expenditure alone might be massive enough to leave them 'starved', weakened and vulnerable.
Circa ME1 this would have been a good excuse, but once again we've had the derelic Reaper that lasted 37 million years powering it's core to stop it from falling into a star. Once at FTL speeds you don't need to expend more fuel, you just need to keep powering the core (Newton etc). I don't think this is a very elegant solution. I would much prefer if they could not fly back at all and instead Haestrom's sun turned into some funky portal they could use or something like that, because at least then it would explain this away well.