That's brutal, but Yosemite weather doesn't play around. You need a fly with a higher hydrostatic head rating, like 3000mm or more. Silicone-coated nylon is way tougher than basic polyester. Just check the specs before you buy anything cheap.

The hidden problem is how these groups create a feeling of unfairness. People see others boarding first for unclear reasons and it just makes everyone annoyed before they even sit down. That social friction actually slows everything down more than any order could help.