So, I've advanced to Tier 2, and assembled the robot thing.
The robot boss is... well, "too powerful" is one thing, but the problem is it doesn't behave like a boss. It behaves like a monster, it's impossible to fight it in anything except either a slugging match (deck out in armor and get a great shield and whack away) or a cheesy tactical approach. I got killed by it a few times, then made use of the planet's soft soil and dug myself a tiny tunnel with a 1 tile opening right under its legs. The Brain Extractor hits it for 17 damage, and autofires. Plink, plink, plink, plink...
It needs a set of "bosslike" pattern attacks and telegraphed moves, so that a player can have a chance to avoid its attacks and use mobility against it. First time it killed me, it just sort of radiated an instakill aura around itself with no warning. Another time it just spat napalm at me without warning. I'd like to be able to fight it like one fights a typical platformer boss - like you fight the UFO, essentially. I had a minimal preparation for that fight, two 1-handed swords and a small dirt arena to maneuver. Took me a while, but that fight was fun! Dodge, weave, smack minions, avoid raining plasma, jump up to hit the saucer a few times, smack more minions, snipe with the bow through a small opening in the dirt ceiling, get out of dodge as the saucer comes down and crushes the little cover, rebuild cover, smack more minions, dodge more plasma, jump and hit it again, etc, etc. It was long, it was probably still a bit too hard to damage than it should have been (you can't really find better weapons than what you craft in 1st tier), but it was a manageable fight, on par with what you can see in a decent platformer like Aria of Sorrow, or maybe UnEpic (it had a superficially similar fight at one point).
With the robot boss, there's none of that. It just rushes forward, and either gets stuck in the landscape, or kills you.