Most comparisons of these two materials are written for the British market, where glass is the default and the prices are close. In North America the entry point for glass is around eight thousand dollars, which changes the question.
Thickness is sold as an insulation upgrade, and the insulation gain across the whole hobby range is smaller than you would guess. What you are really buying is structure.
The rating on the spec sheet is a metric conversion with conditions attached, and it is not the number your local building code compares against. Here is how to translate it into snow you will actually get.