If you wish to delve into the BP canon, when you read up on the profile of Steele, you'll even notice that he was educated in a 'Space War College' that expressly deals with military courses, such as Bachelors in 'Battlefield Psychology' and Masters in 'Strategic Studies', with treatises written on military matters such as warship design. This implies by far, a much greater degree of militarism than any nation we've ever seen on Earth
Those were all actually based on institutions located in democratic nations on Earth right now.

But the GTVA is certainly more hardcore than the UEF.
Why is this the accepted consensus? For the love of me i cannot understand why a civilization which is both technologically and numerically disadvantaged
Whoa, whoa, hang on. The UEF lacks a number of the GTVA's most powerful technologies, but it does have excellent antimatter farms and an enormously capable scientific community. Moreover, numerically disadvantaged? Sol contains population to more or less match the rest of the GTVA, not to mention the corresponding industrial base.
Sol has been colonized for centuries. The rest of the GTVA worlds have been colonized, IIRC, for less than a century - humanity didn't get starflight until fairly soon before FreeSpace 1.
the UEF should be horrifically losing all battles involving capships, but instead we see the exact opposite
We can have a reasonable discussion here, but not if you're going to say things like 'the GTVA horrifically loses all battles involving capships'.

such as 4 frigates and 2 cruisers taking on 4 corvettes, 4 cruisers and a destroyer with ZERO losses (delanda est)
Frigates are significantly more badass than corvettes - the strike package there was specifically designed to do the job without losses. A Karuna is more of a half-destroyer than it is a corvette.
Also, I think you're forgetting an important part of the mission - the job
you did. The UEF has always been described as having a well-equipped fighter corps, and the Wargods were elite pilots. Delenda Est is hardly easy, at least on realistic difficulties - the attack can fail if the gunships don't do their jobs.
(amusingly, the force you're deployed against at the start, is more than capable of tearing apart the Imperiuse and the escort corvette assuming they all start in range)
No it's not. It may look that way in FRED, but I'm guessing you haven't worked in all of their capabilities.
A frigate is roughly the same mass as a corvette (they're longer, but much slimmer), but has some of its space and personnel taken up by a fighter bay and maintenance facilities, so you'd assume it wouldn't perform as well in a direct combat role as a corvette.
The assumption is incorrect. GTVA and UEF doctrine alike dictate somewhere between one and a half and two corvettes as an even match for a frigate.
In the mission before that, we see an Orion with full fighter complement run away from 2 Karunas approaching it in an optimal broadside position for the Orion, yet strangely the Orion jumped out?
Brother...cool down and think about this like a battlefield commander.
Two Karunas isn't enough to take on the Carthage. Not at all. But Lopez is smart. She knows that if she stays there and engages, she's gonna get jumped from another angle.
If we replaced those Karunas with Deimos corvettes, although the Orion would take substantial damage, the plan would be considered doomed to failure. So why are ships with less powerful weaponry seemingly performing better against a souped up version of a ship which would ordinarily kill a pair of Deimos. This puzzles me beyond all belief
Because the Karuna is a more powerful tactical force than the Deimos. Pretty simple. What it lacks in brute force, it makes up for in the ability to blow the hell out of turrets with its gauss cannons and sling antimatter weapons at long range.
Tl;Dr: Peace loving hippies with inferior tech are somehow performing ridiculously well against a higher tech society, geared for war, with nearly a century of constant warfare to hone their skills, weapons and ship designs. Wtf
TL;DR: enormous industrial society with highly advanced technology is gradually losing war to military experts with different but also highly advanced technology and superior combat doctrine.
Makes sense to me.
You just seem to have some fundamental misconceptions about the technological and industrial balance here, as well as the tactical capabilities of the relevant combatants.