Well, I do agree with you that an adjustable head can increase bulk, weight, and failure points.
But there is a payoff: I've used my MC-10 in two situations other than tailstanding.
While trail running, I use the MC-10, and would use a ZL variant with an adjustable head, as a handheld light. Adjusting the tilt of the head while leaving my hand in a position of comfort lets me keep a more natural arm motion, which in turn gives me a more stable platform for the light, and hence a better beam on the trail.
Also, I've used it clipped vertically to clothing or straps. The adjustable head allows me to point the light downward to whatever angle I like. I think the light was probably designed to appeal to military users who would attach the light to a MOLLE vest, and would be limited to a vertical orientation.
I'm not sure how innovative the MC-10 is, it's not the first adjustable angle light out there. But, I've found mine solid and reliable, well designed and executed.
Ted