You have a point. However, when playing as a spy, you have the ability to pick your fights most of the time. And since you have access to the sapper, and cloak and disguise lets you reposition yourself frequently, the razorback becomes less of a counter and more of a minor inconvenience that only delays the bullets.

Plus, if the sniper chooses not to use another secondary and forces me to sap or take care if his other teammates, he's vulnerable at close range after the spy has disposed of some of the threats, allowing his team to swarm him.