Good question. I also have a poly Q5 with a reflex sight and wish I could co-witness with it.New to PPQ and newish to handguns so sorry for the stupid question. Why was this pistol built so that if you put on a red dot, you lose your rear sight? Co-witness isn't a thing with Walther. Thx
Two reasons (besides cost and complexity)
1) Did you see the irons they do put on the gun? Those are a lot nicer than the non-adjustable basic sort you'd get if the gun was trying to allow for both.
As a 5" match gun, the nicer irons are what most people will use, as I doubt most people would put an optic on the gun anyway.
2) Its marketed as more of a competition gun and not a duty gun where the backup irons would be a requirement.