It's got a definite defect, in that the levels of kinetic energy shown in Order of the Phoenix were substantially lower than the "blow up the cottage" level.

But hitting an inanimate object versus a life-sacrifice-love-warded subject, and not being able to precisely measure how much power/concentration Voldemort put into different castings makes it, well, at least good enough for a Dumbledore explanation to the curious in a culture without the scientific method.