I can’t speak for anywhere else, but here in Canada, emergency response team is not a full time job (except in the largest metro areas). Members do regular police work until an emergency.

And even if the cities with full time ERT, they rarely respond as a full team. They are often dispatched to assist constables for other duties. It’s very rare for a full rollout of a tactical ERT team here. And even more rare that shots are fired.

Edit: I am in no way a police expert, but I learned a lot when I worked on a rollout of a body camera program.