I am not sure of Vita's attacks but I think it has Electrical and Gravity attacks. Most robots are weak to electrical weaponry, although you'd probably be better off checking the master Xenoblade X spreedsheet that is floating the net for such values.
This right here has almost all the info you'll need for the game.
Also you might want to buff up your ground game, since the final boss deactivates your skells. That is good offensive skills and weapons, the ones you have. An easy way to beat him might be just the Ghostwalker way with Dual Guns, or element stacking. Infinite Overdrive is great, try to get weapon with Arts: TP Gain and make an Extend Overdrive XX augment (does wonders to keep that overdrive going before postgame).
Also if you use TP arts to deal damage, Candid and Credible Gear has some potential in it, good way to boost damage before you can make the Potential Up XX augments. Not sure if it was level 50 or 55 gear...
You could alternately control Elma, and give everyone Ghost Factory. She also has the skill Hellhound (or some other skill I forgot) which gives her TP with some ranged arts. Executioner is a great damaging skill with Potential armor. This method is probably the easiest I suppose.
Lin can tank a bit I suppose, and Bose deals damage being a simple Partisan Eagle.