I'll be the person that disagrees, at least under certain conditions. Spreading with a spoon it's impossible to spread all the stuff leaving none stuck on the spoon. With a knife that's possible so unless the area is large enough that the overhead becomes small knife makes more sense. Consistency of the spread also matters, if it's sticky or hard once again a knife is easier for the job
I admit it can be situational, for example I still use a knife for peanut butter just because it's annoying to try and get a spoon into the jar. But I'd argue your first point is what the kids these days refer to as a "skill issue" 😉
It's actually pretty effective to use the back of a spoon for peanut butter, especially if you are spreading it on soft bread. I can get the spoon almost clean with fresh (i.e. soft) peanut butter.