No one in this discussion is talking about coasting besides you.

What we are talking about is the slight variation in speed as you go through a complete pedal revolution. When you're pushing down hard on one of the pedals the bike accelerates slightly. OTOH, when the pedals are at the top&bottom of their rotation you can't apply as much force and the bike decelerates slightly. With light wheels there will be a little more of this periodic variation in speed whereas with heavier wheels the variation will be reduced due to the 'flywheel effect' of the heavy wheels having more angular momentum and maintaining the speed of the bike better during the period that you don't apply quite as much pedal force. Note that while undergoing this periodic acceleration/deceleration cycle while pedaling, the freewheel or freehub mechanism never comes into this since at no point do you let up completely on the pedal force and therefore the ratchet inside those devices never clicks.