Since the Flood is a wildcard and the forrunners may as well be, lets give Star Wars one: the little-known Yhuuzhan Vong, who gave both the Empire and Rebels a run for their money. All organic ships, and for shields they use quantum singularities (mini balck holes). Plasma is a popular weapon amongst them too, so there goes any covenant advantage. UNSC would simply lose a numbers war. Forrunner, unknown. Vong have excellent disguise methods for infiltration, and would try "jump to the center of the death star" style tricks because they are just as fanatic as the Covenant. Halo activation is really a "nobody will take us alive" last resort in which everyone loses. Flood, a massacre on ground, but they could hold up in space due to their shield method.
Now, for those of you who are still comparing turbolasers to plasma projectors, consider this: with all the resources available too the Empire, why would they settle for a turbolaser that is weak compared to another weapon? They didn't. Turbolasers are designed to hammer away at star destroyer-type hull and shields, when the hull alone can survive nukes (read about Mandalorian Wars to confirm this). Covenant hull can survive one with severe damage. If a turbolaser can tear through that kind of hull plating, imagine what it would do to the covenant. Even better ranged weapons wouldn't turn the tide considering that 1 star destroyer has 60 of them. Fire enough shots and accurracy won't mean a rat's. . .er. . .you know. . . . Also, don't forget proton torpedoes and concussion+harmonic missiles, which also can be guided.
Don't bring the Forrunners into this when we know so little about their ships and weapons.
Onward to ground. . .
AT-AA's could decimate banshees and phantoms. AT-AT's are the scarabs' equal, but the empire has a lot more than the covenant. As said with turbolasers, Star wars armor is far superior to covenant, so plasma weapons would have little effect on anything, except stormtroopers. Both sides have cloak, neither superior. The Empire has repeating weapons, too, the just aren't used as often. Darktroopers are equal to Hunters, but once again the empire has a greater supply. Star Destroyers can also fire accurrately on enemy position on the planet.
Yes, but we can not forget that the Covenant could shall partly rearm a Forerunner Dreadnought that they had to keep at the low end of it's power because even a station as large as High Charity did not use that much energy.
Here's a quote from First Strike. After considerable study of the Covenant plasma weapons system, she now understood why they glowed before discharge. The stored plasma was always hot and ready to fire, but the Covenant used an inefficient method to collect and direct the chaotic plasma atoms into a controllable trajectory. They selected the charged plasma atoms with the proper trajectory necessary to hit a target and shunted them into a magnetic bubble. The buble was then discharged; subsequent pulse charges herded the plasma on target. For and advanced race, the Covenant's weapons relied on crude brute force calculations and were terribly slow and wasteful. She booted the new system she had devised to control the plasma. It used EM pulsesa priori to align the stochastic motions of the plasma atoms, herding their trajectories and eleven degrees of electronic freedom into a laser-fine columnated beam within a microsecond. This was, of course, an entirely theoretical operation. She test-fired the thre forward plasma turrets-red lines slashed across the black space and intercepted the three lead Covenant cruisers; their shields glowed orange, flickered, and failed. Cortana's plasma cut into the smooth alien hulls. Metal boiled away, and the trio of beams punched clear through the ships. Cortana moved the plasma beams like a scalpel-up and then down-and cut the vessels in half. "Adequate," she remarked. The plasma reserves of the first three turrets, however, were exhausted, and would be several minutes before they'ed recycle. If only there were better electromagnetic system on this flagship, she could have devised a more effective guidance algorithm. Alas, the Covenant's grasp of Maxwell's equations was ironically inferior to human technology. Cortana relized it was fortuitous she had shut down the enemy AI before it leaked her new plasma guidance system. The thought of every ship in the Covenant fleet refitted with improved weaponry was too terrible to calculate. Unquote. And here's another quote. Whitcomb set his hands on his hips," You need to rethink the tactical situation, Governor," he growled." Cortana, find me a target-a rock the same size as this 'gentleman's' base." "Done," she replied. "Burn it," he ordered "Aye, sir!" A lance of plasma appeared on the starboard side of Ascendant Justice, cut through space, and blasted the surface of a three-kilometer-long stone tumbling through the asteroid belt. Its surface heated to orange, yellow, and then white, sputtering blobs of molten iron and jets of vapor that caused the massive stone to spine faster. The plasma cut through the rock in a wide arc-punched through the spposite side. The uneven internal heat caused the rock to fracture and explode into fragments. The debris pinwheeled away, leaving helical trails of cooling iron and glittering metallic gas in its wake. Unquote.
Ah, sorry for the Great Wall here; to much to type. Now since this entire Halo vs Star Wars falls within fan fiction, the UNSC would look at the threat that the Empire is, and hand over Cortana's data. Also, can you find me anything in the books or movies of SW that have one shot from a turbolaser taking out a three-kilometer-long asteroid in one shot. And the Prophets change tech as they see fit, they would take care of the short coming's that Cortana had within months. And please go to Halopedia and look at the Covenant Firgate; it can take control of enemy plasma and send it back at enemy ships, think about the Covenant putting that on all their ships. Also, look to the book Ghost of Onyx, the captured Covenant Destroyer used by the Spartans shot enemy plasma with their own which as it said. Quote. Fred understood what she was trying to do: fight fire with fire. But at these velocities hitting one plasma beam with another was like shooting a bullet out of the air. Unquote.
I will go over the Scarab vs AT-AT and other things like the Vong in the morning. Good night.
This has been a UNSC transmission.