Frankly, most of FF's weapons were good, practical, innovative or thematically fitting. A few need re-tuned, and I think the role of the primary and secondary weapons needs to be re-evaluated. I honestly preferred the ORIGINAL trailer where the conventional ballistic weapon was used more often and the more powerful primary weapon was more limited by ammo; it gave the game a very real opportunity cost for using the bigger gun--something launch-Firefall completely threw out the window with infinite alt-weapon ammo, terrible alt-weapons that were CLEARLY not intended to even be FIRED and just took up a spot as a damned stat-stick, and ridiculous ammo counts for some primary weapons (and let's not even TALK about how ludicrously cheap ammo packs got.)
Specifics? Ok.
Machine guns: yes. all my yes. I was a dreadnaught main. Every other frame I worked up existed for the sole purpose of unlocking perks I wanted on my dreads. Give me huge weapons with big ammo counts and ludicrous fire rates; I'll gladly take movement speed penalties.
Sniper rifles: yeah, I guess these need to exist, but they don't need to completely outperform every other weapon in the game. there need to be times when a headshot just isn't the answer; that way snipers don't become the "DPS" option while everyone else is relegated to being their bullet sponge or healing B%*^#. Up their headshot damage bonus if you must, but for god's sake penalize them against something so they aren't absolutely required all the time. And fix the damn charge rifle; look at Widowmaker from Overwatch for an example of how a "charged sniper rifle" is SUPPOSED to work.
Medic guns/poison guns: I like these because they're versatile. Dragonfly was easily my favorite biotech frame because it could lean so easily toward healing or offense. My melee Dragonfly was easily one of the most hilarious frames I ever played--bouncing from target to target and cutting them in half is ALWAYS fun. Healing needs to be costly somehow, though; otherwise we get the medic/heavy combo going on, and that WILL get dull at some point.
Plasma cannons: of course. Every shooter needs it's grenadier, and the assault was it. Splash damage with an arcing projectile is a great way to develop aiming skills and battlefield awareness; HOWEVER, it does NOT need to have extreme range, splash, power AND ammunition on a frame that ALSO has the best aerial mobility in the game. Have you SEEN a firecat? They never come down.
Lightning guns/repair beams: I know I'm mentioning these in line with FF's classes, but that's the frame of reference we all know. In truth, I actually don't want a lot of 'turret master' action going in. I actually hated the Bastion in FF; it was the laziest, dullest and most unnecessary frame in the entire game, and the bastion players were the whiniest bunch I'd ever seen. Emphasize the variety of function in their primary weapon instead; a lightning gun that can chain to targets, repair objectives or machines, maybe supercharge a frame or some other secondary function would be FAR more interesting to play than yet another multi-turret menace who just plops down a dozen guns and unfolds a lawn chair.
One overarcing design choice I would like to see is this: make conventional weapons that need physical ammo to fire, and contrast them with battery/energy based weapons that have to draw power from the frame to generate ammo. Ammo is costly, but battery weapons can drain your frame of much needed functions. check out the Armored core series for an example of how this relationship can work and when each trade-off is worth it.
At least primaries. They were designed really good and fulfilled their roles. Secondaries were shitty in power, but good in design overall. Auxiliaries were also very nice, but since I am a swordsman, I was disappointed not to see aux weapons as another slot so we could run around with a sword drawn slashing people 
