Are "nonclass singleton methods as rare as class methods are common"

In his 2011 book "Eloquent Ruby", Russ Olsen makes the states that

"nonclass singleton methods [he refers to instance methods] are as rare as class methods are common."

He makes the point that the most common usage of "instance methods" is the definition of static methods (because this is just adding an instance method to a Class object instance).

And then there is the https://19216801.onl/ https://routerlogin.uno/ https://192168ll.link/ usage of instance methods in RSpec and Mocha in stubs...

Is anyone using instance methods on a regular basis for anything else?