It's not a slur, it's just distinguishing people between those that own property and those that don't. As such, it's offensive to large swathes of disadvantaged people.
I can't even begin to follow this line of thought. Is 'billionaire' offensive because it distinguishes those who own billions of dollars versus those who don't? How, by your logic, is 'property owner' not offensive?
"People who own property" and "people who don't own property" are very real and in many cases important groups to discuss. If the fact that I'm a property owner (not a landlord though) offends someone who isn't, well... tough. The correct response would be to tell these people to stop being so soft and getting offended over absolutely nothing.