Honestly I feel the same way evaluating them but still think Cossa is the better goalie prospect. To me Cossa always looks shaky and loose. He's sliding out of position, failing to track the puck and letting things squeak through him. I've seen him fall apart in games. In every way, including athleticism, I like Trey more. He just does it right.
Augustine is 6'1. Most goalies are 6'3+. Cossa is 6'6.
You can't make Augustine taller. He will always be too short. So he has to be technically better than every goalie in the league to survive, a la Saaros. It's a bad bet to make even though he's excelling at lower levels.
Whereas a good goalie coach should be able to fix all of Cossa's issues if given enough time. The things that you can't teach- athleticism and size- are there in spades for him. He just needs to keep practicing. That's why he's the better prospect. I like Trey way more, but he has a much harder path to making it than Cossa.