For wide receivers, there are a ton of other factors. Sammy was super strong at the LOS so he was hard to jam, and he had the speed to blow off the top if you chose to play press. He also has really good feet for route running, and comes out of his breaks with speed. His hands/eyes were also incredible as he was able to make plays on not great throws.
Zay seems to have really good hands, and you don't catch 150+ passes without having some semblance of route running ability. How he handles press man coverage will be a big learning curve in the NFL.
He wasn't a very good route runner, and doesn't come out his breaks with enough speed. That's why he wasn't used a ton over the middle. His hands aren't great, and he honestly wasn't even that good of a deep threat. He had trouble finding the ball in those over the shoulder catches that should be his bread and butter.