Rv, I agree. My feeling is that Hadith elaborate on The Quran (as with prayer).
As for the hardship argument, couldn’t one say:
Hardships are when we need prayer most
Let’s be honest, human beings (men and women) go through greater suffering than monthly periods. It seems silly to think it’s an excuse for that reason.
I’m not convinced we do need to pray at that time, but I don’t think the argument that we are not allowed is very strong. I certainly wouldn’t go so far as to say it’s a sin!