Yeah, the cannon biomech needs to be changed. You're not the only one who complained about it. In its current form it deals like 600-ish damage, which is pretty insane. I might just change it to shoot the nerfed cannonball that the mamut does. Still pretty powerful, but not as extreme.
And man, I am so glad that some people play on easier difficulties. I play mostly on normal and a lot of people insist on playing on serious, so some bugs exclusive to easy slip through. The fight you mention was due to a broken spawner on easy
No dual wielding. Never been a fan of this mechanic. Also no AI texture updates. I'm actually trying to reduce the involvement of AI. Did think about adding the NE Biomech, but the imported model is a little broken and would have to code a different attack mechanic, due to different animations. Maybe if enough people are asking for it.
Not sure what's confusing about the second level, I'm gonna need you to be a bit more specific. Like, I'm thinking that after the floor-to-ceiling crushers, you saw the door open and missed the room that holds the item? Or perhaps something else?