Yes, probably. But that was a rather exceptional situation, compounded, it seems, by several layers of cockup and incompetence. But it isn't representative of general armed police training or response.
Nobody pretends that having armed police shooting people is a perfect situation, or that it wouldn't be better if we didn't have to do it. But incidents with armed police actually opening fire are relatively few, and certainly few in relation to even those situations where armed police respond. Far, far more often, the presence of armed police is enough to cause a serious brown-trouser moment and defuse a potentially dangerous situation rapidly.
So yeah, the de Menezes situation is a serious issue, but it's a completely different issue and isn't at all the point I was making.