User blog comment:James12708/Reapers VS. Forerunners VS. Angels from Darksiders VS. Humanity from Halo VS. Council and humanity from Mass Effect VS. Imperium of Man/@comment-4967682-20130116065115/@comment-3228423-20130116232553

There are a lot of Covenant ships that are roughly the same size as a Reaper, if not bigger. Super destroyers (2 km), RSC cruisers (2 km), ORS heavy cruisers (3 km), battleships (2 km), DDS carriers (3 km), and the massive CAS assault carrier and CSO supercarrier. Basically anything with an energy projector would gut at least 3 Reapers, something that CCS battlecruisers have.

And I think you're seriously underestimating the UNSC for several reasons.
 * They have Slipspace (which is not nearly as fast as ME FTL, but it doesn't require eezo and it bypasses the mass relays)
 * AIs that can easily hack into enemy ships (Cortana could interface and control Covenant and Forerunner tech, who's to say that they can't hack into a computer system they experience for the first time?)
 * UNSC hull armor is not "paper". They use heavy titanium-A armor, and even for a frigate, it's over 2 feet thick. With the marathon heavy cruiser being 2 meters, a UNSC supercarrier being 10 meters, and the Infinity having 5 meters
 * Yes, the Council does have trillions of people in its population, but that's the combined total, so their individual populations are smaller.
 * The Council races are as selfish as they are arrogant, the instant a problem appears that threatens a race the others would almost immediately ditch that race and leave them to handle it. Just look at their history, they kicked the quarians off the Citadel when they asked for help with the geth, they do absolutely nothing to help when the human councilor requests aid with the missing colonies, and of course dealing with the Reapers where they refused to launch a combined offensive.
 * The Council doesn't use WMDs where the UNSC uses them freely
 * The Council is horribly unprepared for total warfare (as proven by the Reapers), not counting Shanxi, the biggest threat that the ME galaxy has faced since the Krogan Rebellions were a bunch of pirates and slavers.
 * ME ships themselves are horribly flawed, they have no coolant which leaves the ships with a limited time to fight before having to flee or be roasted alive, their GARDIAN lasers only have a limited amount of shots before having next to zero accuracy and being unable to fire which leaves them vulnerable to mass missile fire (something that the UNSC often does), as well as having to rely on organics for targetting and the other essentials
 * Orbital Defense Platforms would essentially destroy everything, they can kill at least a half dozen Reapers in a single shot
 * After the war, they discovered a massive cache of Forerunner technology, no doubt they fitted any available technology to all their ships given enough time, the most notable being the Infinity, which was shown running over a ship larger than the Destiny Ascension, maybe even as large as Sovereign, without even taking any damage. It's only going to be a matter of time before they field more Infinity class ships and build ships even bigger than that.
 * Size and ship numbers is something that ME's lacking. The Treaty of Farixen means that they're stuck with only a limited number of dreadnoughts, 39 for the turians, 20 and 16 for asari and salarians respectively, 8 for Citadel humans, and probably 1+ for everyone else. And due to the stupid restrictions by Mass Effect technology, they never get larger than a kilometer; UNSC ships don't suffer from the same restrictions with the UNSC Infinity being over five and a half kilometers long and lined with over a thousand missile pods, 4 MAC guns, over 800 70mm guns and an unspecified amount of dorsal MACs and missile launchers for point defense weapons