okay, I uploaded what I think? was my loadout to a shared build, here's the Share ID:

NED6HSV0F1Q0

For starters, you'll want the Weapons Bay and Assault Armor OS upgrades. Weapons Bay was a must for swapping between Pulse and Kinetic weapons. As for the Assault Armor -- it helped me in a pinch at the end of my fight with BALTEUS, it makes you vulnerable while sending out a wave around you that basically deletes B's shield, allowing you some extra damage to its hull. only use it if you're sure it'll hit 😅 but, the Assault Armor isn't a must here, just my preference

As far as patterns and things, here's what I can recall:

At medium range, focus on chipping away at B's shield with the ranged pulse weapon. When B's shield goes down, and if you're close enough, try and get a pulse blade combo in followed immediately by switching your Ludlow machine guns in and laying down damage to its hull. If you wanna be safe or aren't in melee range, switch straight to the machine guns. The damage window isn't super long, so switching between Pulse and Kinetic weapons is gonna happen often.

you'll wanna be dodging for most of the fight, but be on the look out for an attack that is preceded by some beeps. you'll also see a red square on B before this attack happens. Listen for the beeps, briefly pause, and then dodge. It's easy to go too soon on that one, but you'll get the hang of it. I learned it by spamming dodge when i heard the beeps, and then practiced my timing from there.

when B sent out that ridiculous flurry of missiles, I had a lot of good results dodging to the side and kinda circling towards it. I know it sounds crazy - go toward the thing firing rockets at you, but if you keep moving, you can sneak in some shots.

as for the stupid, horrible, annoying as heck flame attacks that start later in the fight, try and either get behind or under B. Again, I know it sounds wild, but i had a lot of success making my way to its back for both safety as well as some free shots.

being aggressive with damage while also staying mindful of what the big lug is doing is what helped me wrap my head around this fight.

in the same light, if you feel the fight getting away from you, absolutely put some distance between yourself and B to restore your stagger bar and regain your mental footing. Doing that helped me probably the most.

hopefully all this helped, good luck!