Difficulty?

Has anyone beaten the game on hard using only human weapons?

This means only weapons you purchased and upgraded yourself. No alien loot. No human loot. No mission rewards. Only good, ole' fashion human-made weapons.

I've gotten to the final level (and lost) three times now.

Unlike every other mission in the game, it isn't a question of how much damage you can deal. Rather, it's a question of whether you can survive the 10 or so seconds it takes your jump engines to recharge before your flagship dies.

Here's what I've tried
*fighter-heavy - 6x fully maxed out plasma bombers. 2 x resolution and 1 vahalla. Weapons - maxed out nukes. PDW - all shield boosters. Result: absolutely annihilated.
*battleship/ranged - 2xplasma bombers, 2 x liberator and 1 armada. Weapons - maxed out missiles and 2 projectiles. PDW - mixture of bolters and shield boosters. Result: couldn't get through their point defense, slowly got worn down and died
*Hybrid - 2x plasma bombers, 1x bolter drones, 1 x repair drones. 2x liberator, 1 resolution. Weapons - 4 fully-upgraded projectiles (everything to the max), 4 maxed-out nukes. Result: didn't even destroy one station

For the record, I've beaten it numerous times using alien weapons.

The conclusion I'm regrettably drawing is that it boils down to DPS - with alien weapons I can annihilate the battlestations before they can do the same to me.