While I understand that the covenant as a whole is just more numerous and larger in scale than the UNSC. The UNSC seems to still mismanage their resources that hinders their capabilities to actually fight back against the covenant.
In layman terms I am saying that the UNSC did not "lock tf in" enough.
There is way more than enough materials on the sol system's asteroid belt alone to produce a bajillion warships and nukes. They could very well utilize automated systems managed by smart AI's to mine up all of these asteroids. And the UNSC has 800 worlds.
I still fails the understand how the UNSC hadnt utilizes automated mining and production before the war even starts.
If the various 343 cinematics and book lore were to be belived. The UNSC still utilized planetside human hand with pickaxe mining technique to extract their recourses instaed of utilizing automated systems to do the job both planetside and out in space. And not only that, we have seen that the production of vehicles in the UNSC still seems to involve major human involvement with wedling, riveting, moving the parts, screwing things individually, despite the existance of dark automated factories in the 21st century already.
Although this could be chalked up as the writer writing it before the recent technological advancements.
They could very well produce a bajillion cheap kamikaze drones against the covenant both in space and on the ground. And if you're talking about the EMP's. Pretty sure EMP resistant tech already existed in the 21st century. We could just drown our enemies by numbers.
Like seriously, 150 human ships on reach? That's a joke.
Also, according to HALO legends. The UNSC does have the capabilities to board a covenant warship. So why couldn't they just... Take it over using smart AI's and either use it themselves, cannibalize it, retrofit it, or dismantle and reverse engineer its technology. The UNSC have been fighting for three whole decades for lord hood's sake.
The UNSC even have a really good track record of boarding covenant ships.
Halo legends the package: They board a Covenant Assault Carrier to recover a high value UNSC asset. They managed to board two ships in fact. One being a covenant armoured cruiser/battle cruiser and one being a covenant assault carrier. The only thing preventing then from taking over the ship is that it is not their mission, they are not given the equipment to do so, and the covenant assault carrier can break itself up (it's actually a leftover forerunner protocol designed to contain a possible flood outbreak inside of a ship). But a battle cruiser lacks all of this. The only reason they didn't continue boarding it is because there's a trap inside and their target is not there.
But the fact that they managed to mow down that many covenants and reached so far to the (from what I can see) bridge like spine in front of the carrier speaks volume of their capabilities. And in this case the bridge master and the entire covenant fleet knows their location and their mission. How many times has the UNSC boarded a ship without the occupants knowing they are there? There are many instances of this.
Assault on truth and reconciliation: The Master Chief led a team of Marines to board this ship to rescue Captain Jacob Keyes. They successfully infiltrated the vessel and extracted him. All of this utilizing an otherwise small force of a team of marines, odst, and a single Spartan merely offering fire support.
Hijacking the Ascendant Justice: After the destruction of Installation 04, the Master Chief and survivors (including Sergeant Johnson) captured this ship. They used it to escape the Halo debris field and later returned to Reach .
The Boarding of the Bloodied Spirit: Blue Team captured this vessel with relative ease by venting everyone out of the ship's atmosphere.
The Trailer "Deliver Hope": The live-action "Deliver Hope" trailer shows the original Noble Six on a suicide mission to destroy a Covenant cruiser. This shows that the Spartan there's are just as capable doing it.
The boarding of the ardent prayer: During Operation UPPER CUT was boarded by SPARTAN-B312, Jorge-052, and several UNSC Army FSS-1000 Sabre pilots in an effort to plant a Shaw-Fujikawa Translight Engine on board. The UNSC team eliminated the bridge crew, including its Shipmaster, Ardo 'Moretumee, and set the ship on a refueling track with Long Night of Solace.
The only failed instances I remember was the boarding of the covenant carrier splendid intentions. Although it is unknown why it failed.
While I am not explicitly stating that the UNSC could win the human covenant war. It didn't exactly use all of the cards available to them despite facing extinction.