A taser is basically ineffective when used on somebody high on PCP. If they're violent enough, you basically either need a tranq dart or a gun.
Meth is a problem everywhere yet cops still manage to apprehend suspects without anyone dying of a drug induced heart attack in the process.
And I swim all the time without drowning, yet swimmers drown all the time. So what?
This isn't a software function, there are thousands of factors involved and a cop is walking in knowing a handful. I don't think you're being realistic.