I think yall are too exhausted from this story. I chose to take it as: the mc weakened the boss, cutting it in half is no small feat and requires a lot of energy to come back from. It's not that the MC is weaker than the crafter, it's that fighting a raid-boss alone is crazy.
The crafter came up with a giant golem and smacked the boss away, she didn't one-shot it. They're going to defeat it together.
The whole point of this arc is to show that they cannot win alone, no matter how much of a singularity any one of them is...So I don't really get the complaints about the power levels.