Do these dead balls affect flight path and launch aswell ?
How to get rid of the nasty impact marks they leave ?
Yeah, range balls are built for durability and don't have the distance of regular balls. At the range I go to they don't have enough space (housing development behind) so they have 80% flight balls and a net. So your range balls may be purposely deadened to limit flight.
In general I use range work for working on some aspect of my swing and ball striking, not gauging distances. When I find a real ball in the mix I use that with an PW to see what my adjustment should be up through the progression.