That’s literally what russia do with their variation of Iranian Shahed drone. It costs way less than Patriot’s PAC3 rocket.

Ukraine has mobile AA groups with vehicle-mounted machineguns and a new invention, antiair drones. This allows to reduce the use of PAC3.

So yea it’s a working tactic. Moreover, I would say Europe isn’t prepare to counter it. USA is only comfortable vs Iran cause they are several oceans away.