So what are you asking? Do you think the tie downs set the carrying capacity or GVWR of a toy hauler? From your post it seems like you do think the tie downs effect the carrying capacity (CC) of a toy hauler which is not the case at all. The frame and build of the trailer plus the amount of stuff added to the frame of the trailer set the end CC of unit.
Does each tie down in your trailer have a 2500 pound capacity or is it 2500 pounds combined and if combined how may tie downs do you have? So what if the tie downs are not attached to the frame, on most atv or motorbike trailers I have seen the tie downs are screwed to the decking and I have never seen one pull out. Heck I have even hooked a winch to the tie down point and winched broken down ATV's onto the trailer.