Skill issue.
The triangles move slower if you're close to them, so if you edge them, the enemies aren't a problem while you fight the boss. You also need proper upgrades like multi shot and wall punch for the first boss to be easy. You need to reroll shop to get them. You can't try to save your creds by not rerolling, that's dumb.
You need bellow perk for smiley and piercing upgrade for the second boss. The third boss takes a while but if you have enough speed you can run through the slime without taking damage.
(Although I also find it a bit annoying when I can't push one side of my window sometimes after using Bellow. )