Whether it scratches your paint or not depends on so many things: how often you clean the bike, whether you take care cleaning the underside of your tank bag when you remove it and put it back on, what type of riding you do, etc.
I had this on my bike in Africa, a Giant Loop tank bag with a zippered mounting system which stayed on the bike:
That mounting system stayed on the bike for the entire time I rode it, about a year and a half. Never removed it, even for cleaning. During that time, I rode through every terrain imaginable: sand, mud, gravel, pretty much everything an ADV bike should be ridden through.
When I sold the bike, I removed the tank mounting system and the harness had taken off the clearcoat:
You can see the difference in the the shiny spots on the tank and where the harness had rubbed on the paintwork.
*shrug* it's an adventure bike, not a show-and-shine Harley...