The way the human eye works is it tries to automaticaly center curves with each other. Straight lines you find in leaf rear sights dont seem to be affected by this phenomena. Thats why the sights like peep sights work best.
Its a non issue brought up by someone thinking too much with no experience.
My scar17 has hk style front peep rear with an adjustable front sight post. It works just fine no problems. The only issue i have with hk style front is i have a harder time cleaning the front sight post area because of the full circle front. Functionally it works just fine
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith