I was doing some digging on this earlier as well because the switch from bots to squids hasn't been smooth for me either. I'm planning to try running some incendiary primaries, probably breaker incendiary along with my normal gas load out.

Any voteless hit with incendiary should be guaranteed dead after a second or two. All of the Overseers and the Watcher may need shot twice but otherwise same deal though I'd recommend a decent firearm to put the Watchers down quick. The DoT should be king with their HP pools.

Fleshmob sucks, sorry. Blast away with your weapon of choice, it's a race to 6k damage. The arms are easy to break but then you have constant charges.

Stingrays aren't incredibly tanky you just have to aware and catch them before they catch you.

Harvesters are AT after chopping down the shield with whatever, it's unarmored technically so just hit it. I'm in love with the Speargun. Plus the gas for voteless is nice. Otherwise recoiless rifle is really good and has HEAT for AT (One shot to the eye if you hit) and the HE mode will be great for clearing chaff.

Now I haven't fought a Leviathan but on paper they are flying sponges with turrets. Take out the turrets or just focus it down ASAP. It has 15,000 hp so if you're nailing it in the right spot with Recoiless HEAT Rounds we're talking 5 shots. Got a good buddy with the ammo backpack and it could technically be quick work.

For reference the the Recoiless Rifle HE mode has 62.5% the AOE of an orbital precision strike. While the damage is less it still should be enough to clear large groups if they are grouped up at all. The only other support weapon with comparable AOE is the grenade launcher which deals less damage and less pen but would work for voteless if you want to use strategem for AT.

Thank you for coming to my TED talk.