PLD's Spirits Within is an oGCD attack. Its damage is boosted by Fight or Flight. Weave it between GCDs.
WAR's Upheaval is an oGCD attack. Its damage is boosted by Berserk. Weave it between GCDs.

I'll just take it that way and I'm good to go~

Onslaught can be used as gap closer or an offensive oGCD just like Upheaval.