kfcho- Man, I'm sorry you're having all this trouble with a new car. Must be getting frustrating.
The "disadvantage" is that if you remove too much clearcoat (maybe anything more than .3 of a mil, as I recall) you will get clearcoat failure and then you're looking at a repaint. You really shouldn't have to remove THAT much to get the flaws out, but you don't want someone to botch it up, either. And it's pretty crappy that you have to even think about this with a new car. If you take off that much clear now, you might limit yourself to what you can polish off later if the car gets swirled/scratched. Maybe no biggie, but you're sorta limiting your long-term prospects right off the bat.
I get the feeling that a) you're not about to do the job yourself b) you're getting fed up with this c) time is passing and the sooner you deal with it the better.
You won't like this, but if I were you/it were my car (actually, if it were mine I'd go at it with my PC and/or Cyclo and take 'em out myself), I'd consider telling the dealer you can't get the marks taken out without killing the clearcoat (show them the receipt from the place that tried) and you want a new car/refund or you're going to turn it over to your attorney or the local business owner's association. Then do it. They've already accepted responsibility to some extent by being willing to pay for the repair, that should help. You're starting off your ownership experience on the wrong foot and they oughta be held responsible. Let 'em sell it to someone who doesn't care. It's sorta throwing in the towel, but hey, it's something to consider.
But as so many have said, the marks SHOULD polish out without too much trouble..as Nagchampa said, you need to find a better detailer or get the stuff and do it yourself. Get it fixed or get it gone. Just my $0.02, of course.