Earlier quoted context omitted.
I do believe you are correct (I remember the same thing). People use what they have, but being dead from a knife is still dead. I find the rate of various crimes important as opposed to the tools used. Tools can be substituted.
Tools generally only have partial substitutes. (From memory only...) Suicides decreased in the UK when catalytic converters became required on cars: other means of suicide remain available, but most are harder for the potential suicide than sitting in a car with a pipe from the exhaust through the window. Knives are substitutes for guns, but it's harder to kill 10 people with a knife than with an automatic. Which may…
Killing one person with a knife is not harder than with a gun. A criminal willing to kill is going to do it with one, or the other, or both.
Just look at the UK. Violence is bad and there is a total ban on handguns and a near total ban on just about everything else (many restrictions and you need a purpose to own the gun - self defense and for "fun" are not reasons - eg. farming, deer huting, formal target shooting )