In my search, I found that they spend almost an equal number of hours in air like you said - 75-100 hours per month. If that's the case, after adjusting for sex, these numbers holding would throw some uncertainty into the radiation hypothesis.
According to a bit of Googling (which included LLM responses so if you need to be sure verify what follows), although flight attendants and pilots spend about the same amount of time in the air and so get the same exposure, flight attendants have fewer rest requirements and scheduling protection. This results in them working more erratic shifts with shorter rest windows, which results in more circadian rhythm disruption than in pilots.
Important mechanisms in the body to suppress tumor growth and repair DNA damage are linked to circadian rhythms and are less effective when those rhythms are disrupted.
