Despite Hackett's insistence that we couldn't I can't help but disagree. There seems to be a tonal shift in ME3 wherein somehow the Reapers are stronger than we'd anticipated despite the fact that the galaxy has been adapting and using Reaper tech for years now. I a mean come on, with the introduction of the Thanix Cannon in ME2 you'd think the Turian and Alliance fleets would at least be on par weaponry wise, yet we don't get to see a Thanix fired once.
Fleet wise I guess it's really anyone's call but I've got to think the Alliance, Turian, Geth, Quarian, Asari, Salarian, Terminus, and the other species couldn't have overwhelmed the Reapers barriers. I mean come on now, we're talking tens of thousands of ships, many of which, according to the codex should have Thanix Cannons.
On the ground I don't think there's really any question as to who would have supremacy. We're talking the full brunt of the Alliance and Turian marines, Krogan Battlemasters riding dinosaurs, Geth Primes working side by side with Quarian marines who have Geth AI in their suits, Asari Commandos, Salarian STG operatives, Drell assassins, Elcor with rocket launchers and mini-guns strapped to their backs, wave upon wave of Vorcha and Ymir mechs courtesy of Aria. And that's not even counting the fact that there's no way the Rachni would have been shoehorned into purely a construction role.
"In the case of a Reaper capital ship, these kinetic barriers can hold off the firepower of two dreadnoughts simultaneously, but three clearly causes strain, and four typically results in destruction. Weapons designed to maximize heat damage, such as the Thanix series, show better results against the Reapers than pure kinetic impacts. "
"The barriers of a Reaper destroyer are less formidable than those of a capital ship. It is possible for a single cruiser or many fighters to disable or demolish a destroyer if they can get within range before they are themselves destroyed."
Now the Council races (plus the 1 Volus) have 85 dreadnaughts, with the Geth quoted as having almost as many as the Turians (39, we'll say 30 for convenience) and since we don't get any hard facts regarding how crazy the Quarians went as far as arming their ships we'll just say they have 5 dreadnaught capable fighting ships. That brings us to 120 dreadnaughts total. Let's be generous and assume that half of those were wiped out before the initiative to retake Earth. That's still 60 dreadnaughts.
The mistake people make is to assume that dreadnaughts would be the decisive factor, but they wouldn't. Considering humanity's loophole around the Treaty involved making carriers which could go toe to toe with dreadnaughts we have to consider those would play a huge role.
The Reaper fleet has only ever been quoted in the thousands, and according to the Codex only a small percentage of that are actual capitol ships. The combined allied fleets have hundreds of thousands of ships. Using tactics like the Turians did at Palaven with tens of thousands of ships would have no doubt yielded better results.
"Knowing that the Reapers' weapons had a longer effective range than any of his own, Coronati made a short, daring FTL jump--landing his dreadnoughts in the middle of the Reaper fleet. The dreadnoughts then turned to line up their main guns on the Reapers, which also needed to turn to fire on the turians. This ploy used the Reapers' size against them--because they could turn faster, and their concentrated firepower downed several Reaper capital ships. "
Reapers simply would be able to target allied ships fast enough without being overwhelmed.
Plus you can't really count Sovereign as an indicative Reaper engagement, considering the galaxy had never faced anything like it and the Destiny Ascension probably never sweated another ship since it was built. It's akin to World War I, so destructive because the tacticians were using old world maneuvers with new world factors in play,
/nerdvent