Yes it is very easy to take out the Europeans, but do you want to?
They always seem to start in dumb places, typically right next to a native village, and you cant seem to raze them. So you get stuck with a city in a place you really dont want it, plus you usually get another free colonist, which is nice.
Also there is always the chance things will go bad, for instance the natives might declare war (-2 You declared war on a friend, -2 you stole our land).
Not saying its wrong to take out the Europeans, just not as obvious as it might first appear.
There really ought to be some game mechanic that makes it difficult to eliminate the other Europeans. Like the warriors +25% city defend. Maybe an enforced peace for the first few moves.