Draft collar, better fit to shoulders, differential cut, trapezoid footbox.
You get what you pay for, .. .or...in some cases you dont.
Without a doubt quilts are better than bags in every single way..... Except warmth. That's the one that counts the most. The simple fact is a quilt needs a greater thickness of insulation then a bag to be as warm as the bag is. And, you need a head covering. With the extra extra wide sizes all these people want to get today, you're not saving any weight at all. And they're not as warm either.
And that's fine, until somebody expected to be warm to rating, and and they're not.
I added 1.5 oz of down to my 20 F quilt. To make it near-er to 20 realistically.