"have increasingly charged sexual assaults in the least serious category, from 88 per cent of cases when the three tiers of sexual assault were first enacted in 1983, to 98 per cent today. "
Well first the police make arrests. It is the crown that decides what charges are brought to court - they can opt for more serious or less serious if they want.
Second, maybe there are more complaints of sexual assault that don't involve rape (which imho is what most picture when they hear the term)... maybe more women or pushing for charges on the less serious infractions. We don't know because for some reason the authors neglected to include that information.
And " Police data send a message to the public that 98 per cent of sexual assaults reported are of little consequence."
Please, they do no such thing. Everyone I know thinks rape is a very serious crime that should be prosecuted.