You have to be technically competent, proficient.
You do not need to be technically perfect.

From your statement, if at heavier weights, a boxer can have knockout power in one punch, does technique not matter as much.

If he is not technically sound, he will not transfer the weight behind the punch so is not being efficient at punching, not maximizing his power.

If he doesn't have technique in his footwork he will not be able to move in to a position to land the punch.
If he has a flawed technique he may be off balance to defend a counter or deliver a follow up punch.

You also need technique to avoid or block a punch. As Manju stated.

Not every one is going to move or punch identically to another boxer, and there will be variations in a left hook for example.
But if you don't have the basic technique you will be making life very difficult for yourself.