The last time I remember having a guy of that size used like that was Noah Hartsock and that turned out pretty well for us. Yes, when a 6'9" guy shoots from the perimeter it takes him out of rebounding position but it usually also takes one of the opposition's bigs away from the basket, too. I won't claim to be a great basketball Xs/Os guy but I would guess you'd use a guy with this size and shooting skill differently depending on how defenses are playing you. It seems more effective to bring a shooting big out to the perimeter more against man-to-main defenses than zone defenses, because then you bring the other team's big with you whereas zone D allows opposing bigs to stay under the basket, which would support your point.