The "got flamed by two old timers" part is funny because those guys probably learned on lacquer with a wool pad and never touched a DA in their life. What nobody talks about is that grit ratings are not the same across brands, so your 1500 might cut like their 1200 or their 800, which makes the whole argument kind of pointless. Judge the finish with your own eyes under good light, not by what grit number some guy yelled at you from across the shop.
The grit number fight always cracks me up because it's just two guys comparing sandpaper from different companies. You're right that @the_linda has the only take that matters, look at the paint, not the number on the back.