With a scope the front sight is a grey blur at 3X that, for me anyway, pretty much drops from consciousness when I'm sighting with the scope's reticle. At 4.5X and above it disappears altogether.
With a red dot/holo sight you can set it up with a "perfect" cowitness, where the dot is aligned with the iron sights. That is how I have most of mine. The beauty of the red dot, though, is that if having the dot on the sight post bothers you, you can move your head a little and the dot moves off the sight post but is still on target.
That arrangement bothers some; alternatives include using risers/mounts that position the iron sights in the lower third of the red dot window, or using fold down front and rear iron sights.