You can obviously reach higher maximum values by going solely into a single element, but then just as obviously you will fall very far behind a different pure build on different targets.
But that's the beauty of Fighter stances: they boost all tech damage no matter the element. So not only do they completely obliterate the specific targets you're specced against, but anything you didn't directly counter will still take heavy damage often on par if not surpassing that of a generalized build.
After the Stances, only Chase Advance Plus (not Chase Advance itself) will directly increase your damage, but Knuckle Gear and Step Attack let you move much quicker than anything Force could do on its own, Adrenaline makes a quick uncharged buff into a full 60s duration, and Crazy Heart makes even Caves tolerable to run by giving you such ridiculous PP regen rivaling both Techer and Gunner's PP passives combined, though it's only during status effects.
For Braver, Average Stance is less damage than Brave, so there's little point in bringing Fo/Br to areas where you can't target enemy weaknesses, but there isn't much else that can benefit a casting class other than the two stances.
A Techer subclass, if not used for its own Masteries, can supplement Force's elements rather well. For Fire, max PP Convert can help sustain the high PP cost of Nafoie and shorter charge times on them all. For Lightning, max Territory Burst makes Zondeel extra devastating, and then TBPP Save along with the other PP skills make the already cheap techs even cheaper, so you can afford to take points away from Bolt PP Save and instead max Tech JA Advance.