I understand the concerns of the OP. How can a rental car company claim non-responsibility of a parking violation? We can't do that, the owner of the vehicle is always on the hook. Is something written in the vehicle code that allows a rental car business to do that? Also, how can the DMV's pursue someone with a warrant based on the accusations of a rental car company?
Seems to me that the DMV's and the collection agency would make threatening gestures, but in the end, have no teeth. Their only legal violator would be the rental car business but they give them the pass out of courtesy.
I believe the advice the OP got from the traffic dispute specialists.
Example: If you legally drive a company vehicle or truck, get a parking ticket, who is on the hook for it? Answer: The registered owner.