I’m totally confused by this conversation.
There are numerous maar mikomos that explicitly say that sometimes (these are exceptions, not the rule) punishments are not necessarily a barometer of the crime. Rishonim explicitly say this regarding naara meurasa versus a regular ashes ish (while others argue). rape will also always be classified as a gezel, Thus it was included according to the rambam in the sheva mitzvos.
in regards to intermarriage to nidah, rav sadyah goan as quoted by the iben ezra says on lo sinaf says there are different levels of sexual avaras the lowest level is being with a unmarried woman, worse than that is to be with your wife when she is a niddah, worse than that is eshes ish, worse than that is to be with a non jew, worse than that is homosexuality, worse than that is bestiality.
We must also never take an agada statement to lessen halacha though, which seem to be what this fight is possibly about
Just like separating halacha from agada is antithetical to Judaism (see marahsha hakdama for small point on this), We must always remember that the birth of Christianity was taking agadah without halacha.