Never said knives were less dangerous than guns just that an assailant swinging a knife can do damage, but if your argument is that if get rid of guns we can get rid of mass killings, then may I direct your attention to the 86 people who were killed by a truck.
We regulate trucks more heavily than we regulate guns in the US, and the cost/benefit analysis is substantially different.
Truck driving has a minimum age, a licensing requirement, registration of the vehicle, often annual inspections of it, etc., in part because we recognize their potential for danger in the wrong hands. Very much not the case for gun use.
https://en.wikipedia.org/wiki/2017_Las_Vegas_shooting