This is an issue of mine that truly bothers me: The Reapers and their strengths. Let’s look at the past facts.
Sovereign’s attack
In the Battle of the Citadel, Sovereign, being the smart/cowardly villain, it was immediately performed a blitzkrieg on the turians, ramming any ships in the way with its shields taking the brunt. After that Sovereign than latches to the Citadel Tower and closes the arms, safely protecting itself while the geth fleet faces off with the Citdael Fleet. Ultimately this means by the time the Citadel arms open and the Alliance goes up against Sovereign alone, without help from the Citadel fleets, which are too busy fleeing or trying to help the Destiny Ascension to help (Not the turian fleets were not all their, so it makes sense they still have military power over the Alliance).
The Alliance Fleet(s)?
What were the fleets attacking Sovereign? Joker states in ME he is with the entire Fifth Fleet with him and that makes sense considering the Alliance are still at war with the geth and another fleet may attack Arcturus Station. So a single fleet took Sovereign down, which makes sense in conjecture with Shepard’s actions. It is a show of great power, but not invinciblity.
Now take a look at Mass Effect 3. Hackett says that beating Sovereign took “everything they had” and the war assets claim the First, Second and Fifth Fleets participated in the battle, leaving a lot of their territory vulnerable in a time of war. This is a massive and strange retcon simply to make the Reapers seem more powerful and allow the Crucible to justify its existence.
War Assets
As a greater example of the retcon’s lack of sense is that in the war assets it claims each of the three fleets mentioned above lose a third of their ships (if you saved the Destiny Acension only). But we know the ships lost. Eight crusiers. Shea, Emden, Jakarta, Cairo, Seoul, Cap Town, Warsaw and Madrid. Give or take a frigate or two and the fighters which in this case are negligible.
Now think about this. Eights crusiers make up a third of three fleets? That would mean each fleet lost about an estimation of three crusiers each if we round off. By that estimation a single Alliance Fleet is made up of the respective firepower of nine crusiers. NINE CRUSIERS? How do you defend a planet with a fleet with that kind of limited capacity?
Let’s be fair and take this further. The First Fleet lost 55% of its forces to the Reapers at the start of the game. So it realistically should be a war asset of 200. If a third of that (66 war assets) is the equivalent of 3 cruisers (the war assets say a third of ships are lost, so I assume the reason the asset loss is -25 because the Alliance built a few cruisers to make up the loss). If we take these and other war assets into account, the a cruiser is 22 war assets, a dreadnaught is 50 war assets, a frigate is about 15 war assets and a carrier is, well we don’t know (lets say 30 for clarity).
So, estimating that one fleet has one dreadnaught. So realistically the First Fleet has about one dreadnaught, one carrier, three cruisers and three frigates. That is simply nowhere near enough to buy as capable of defending a planet.
Other things that annoy me
Did you notice that to make this more and more hopeless, the Reapers, when on screen, are completely wiping the floor with the turians, blowing up “two dreadnaught in one hour.” And yet we are expected to believe they are “holding out.” What does that mean? Are you just standing and waiting while the Reapers blow them up one at a time?
And did you notice that we never see a Sovereign class Reaper die? Ever. Not one. The closest we get is one that loses an arm, only to blow up a ship afterward, so it’s not going down.
In the end this is an obvious case of Bioware trying to build the hopelessness, but is overdoing it to the point that the plot is suffering for it and the Reapers appear, not only more powerful then Sovereign, but also over powered.
EDIT: Another thing is that the weapons utilised against the Reapers seem not to be as effective as they should be. It confuses me that they don't leave a scrach and don't seem to bother the Reapers shields that much.
At this point the fleets have nuclear weapons, Ferris slugs that implact with the force of a 38-kiloton bomb AND this cycle has the Thanix cannon, which took out a Collector cruiser in two shots. Seriously the fleets should be doing a lot more damage with that kind of armament then they seem to be.