yeah, it's possible to solo. It seemed you were doing well so far, don't worry too much about the machines they'll always come back, just go after the boss if he's on screen.

Aren't all boss fights in this game multiple waves? Even minibosses such as the Big Iron.

Probably you gave up just because it was getting too stressful? Try going back again. Everything is much less intimidating the second time. :)

As others have said, the mission can definitely be solo-ed. I use Acheron and a shadow gun. An elemental weapon would help against the occasional constructs, but shadow is quite adequate.

The dungeon as a whole is pretty tough if you're solo, but still manageable if you play right. But the actual fight with Seerus, man... the endless barrage of missiles, taking out the battlepods to bring Seerus down which requires you to get RIGHT in front of the missiles' path if you use swords or bombs, and Seerus himself, getting WAY too crazy with all the Dark Reprisal bombs. It's hard with a team, but completely insane when you're solo. I wasted more Sparks of Life in that boss fight than I have anywhere else in the game. It's clearly built for a team, unless you think you can manage taking on that juggernaut of a boss.