The GTVA needed ancient 5-legged cyber-organic killers with plasma accelerators built into their carapace to defeat them. The Empire required some kind of pre-historic Care-Bear....
Lies!
Many Bothans died to deliver the information that led to the Battle of Endor! It was just that the Care-Bears stole the show and Bothans get one sentence in the whole movie series referring to them.
Than again, a bunch of teenagers and an aluminium falcon was enough to blow up the first Death Star.
That said, it's possible that the Imperials have resources comparable even to Shivans. I mean they rule a galaxy. GTVA covers about 20-30 systems (drew the number from my hat, might be wrong, might be right, failure to care imminent) and are reliant on nodes for intersystem transportation.
Then again, terrans and vasudans seem to be very good at stealing and adapting foreign technology to their needs, seeing how they managed to adjust their sensors to detect Shivans in about two mission time gap, get working primary weapons against Shivan shields very fast, and the assimilation of Shivan shield tech was also incredibly fast and the technology was also manufactured and fitted on the ships at unbelievably good efficiency. I mean, in one mission you save the prototype and in the second all your ships have shields - I have to hand it to the GTA/PVN logistics, they should probably be assigned to high command as well (but then the good logistics would be lost...)
But, as was said, as far as fighters go, GTVA has much better equipment. Bombs seem to be more powerful, although imperial missiles have more advanced homing capabilities. But Imps have more fighters and bombers so they can deal with them being practically mobile weapon platforms for a pilot in EVA suit.
In cap ship battle, Imps have better mobility (assuming they can use hyperspace in GTVA space) and better defences. Oh, and they have more of them too. Nevertheless, aside from Death Star/Eclipse superlasers, GTVA ships have better long-range weapons (beams), but their efficiency against Imperial capship shields is up to anyone's imagination.
The biggest problems the GTVA would have against imperials would likely be numbers and hyperspace's advantages compared to nodes. In equal battlegroup engagement, I think the fight would be pretty even, but the fight is only one part of war - the imps would never have need to fight on even grounds, they could maintain their presence in GTVA systems very easily and simply land some huge amounts of ground pounders and stormtroopers to invade the GTVA systems before the node-dependant GTVA forces could even respond...