That isn't the main justification. It is simple supporting evidence, that might be comparing them. She injured and force down a Near High-End Nomu, that is as strong as Hood. We don't really know how effective it was, so we place her at 550 MT.
That is fine for a possibly rating, your biggest argument against this is a fallacy. You can't believe Nejire can be that strong, so you disagree. But that isn't how we work, she has a possible feat, so she gets a possible rating. She downscales because we can't tell the extent of the damage.
I apologies if that came off as aggressive, I don't mean to offend, just getting tired.