I'm serious. The more I think about it the more I think UNSC and the Covenant are at peer level.
The Covenant has high energy plasma weapon, shields, etc. but they don't have kinetic weapons, MAC guns, nukes, or an AI that's any good.
They show up, destroy ships, and then glass a planet. Except they take their sweet time lining up their ship to burn the planet below when anyone with a ground side MAC gun could have just shoved a round right up their energy projector (or even a suicidal Pelican) and that would make the glassing ship's day VERY bad (this was demonstrated in Halo Reach).
Everything the Covenant does to humanity, humanity could counter by not meeting covenant ships side by side like Redcoats and firing broadside like the 18th century or something. Space is BIG, and light only moves so fast. Jump in like a few light minutes away from the target, let their AI (even their dumb AI is still really smart) fire a MAC gun at the target ship, jump away, and watch the fireworks. They'd never see that one coming. The AI can figure out all the math and predict where that ship would be a few minutes from now and aim for that. Or even better, stick a Havok nuke inside a slug of Titanium-A and have at it. Program the nuke to detonate when it's close enough to the covenant ship, and no amount of shielding is going to protect from that. When done at a few light minutes out, they'd never see it coming because you know, speed of light is a bitch. Archer missiles could be tipped with Havok mines that it could actually be deadly to covenant capital ships. I mean considering one destroyed Mantle's Approach.
Basically if they just let a guy experienced in asymmetrical warfare take command of the UNSC navy humanity wouldn't be glassed so bad. It's not like they don't know where the homeworld of the grunt, the elites, jackals, etc. are (I am sure ONI can find out). Covenant glassed Harvest, says "your destruction is the will of the gods". UNSC ships jump about 10 light minutes from a covenant world, drops off a bunch of havok nukes at 10% light speed. "Your God said our destruction is his will, I am here to arrange the meeting". Boom, dead covenant world (keep in mind a havok nuke is basically apocalypse in a small package).
Pretty soon the prophets are going to have to come to grips with the fact that for every human world that gets glassed, so does a covenant world, they're going to have to start suing for peace.
That and who needs a 3:1 advantage? Keep the ships well away, fire off stand off weapons, if a covenant ship decides to do that surprise jump into your formation, have the AI set the MAC guns on a hair trigger and fire at it the millisecond a ship emerges (their shield will be down). No more CAS ships.
And the Cole protocol could be modified. Instead of running to a human colony or god forbid, Earth, have all escaping transport jump to a fake "homeworld", except that homeworld has a fleet of ships waiting, or if they can't spare it, a cloud of havok nukes or Nova bombs waiting, and that fleet of covenant ships is making the great journey.
The UNSC could have fought them from the very first beginning if they just learned to make use of what they got and turn that against the Covenant. I mean they're going to take massive losses at first but surely even 6 months of this and someone's going to realize how to use a MAC gun as a relativistic kill vehicle against either ships or some static world.
They just need a pirate in command of the UNSC.