It is indeed hard but doable, starting out its best to swap for a full health vulfighter before you get closer to the end as well has hold on to those omega weapons as last resorts.

Hmm, I would have liked (for the final boss at least) that the remaining VulFighters joined the fray each time I am losing one or something.

Guess I gotta hit training mode and learn the final boss. But this is definitely keeping me from trying hard or superhard mode.

The game is medium difficulty i think, even easy if you compare it to other games in this genre.

Yeah, it's really aggravating to lose at a point like that. My only advice, at least on normal, is to let the Vul-Fighters get repaired to full before using them again, and try to keep the Drill one in store for the final boss. It helps immensely, especially the charged shot.