To be selected it comes down to many factors.
I think you didn't formulated questions right. Yes, legion prefer lean guys over bodybuilders because legion (or any modern army) men physical requirements are not really suited for muscular guys who need 30 egg whites, 2 kg of meat and coupled protein shakes (Im not even mention cocktail of chemicals that many of those guys take)
That's right. All that muscle spending lot of oxygen also you have to carry all of that wight. Not good for staminaTo be selected it comes down to many factors.
In regard to your question, a lot of "heavy muscled" men have not a whole lot of stamina, which could be the reason for rejection.
Check up on the Luc-Leger test.