You're being dishonest here. In the normal word, 4/5 isn't "sucks". Neither is 3/5, really. But if we rate our servers 4/5 or 3/5, Disney sees that as "sucks". Servers are expected to have a 95% average after each cruise, which allows for one 4/5 rating for every three 5/5 ratings. Anything less is considered unacceptable to Disney.
So, sure, if you have a terrible server, then you might not mind saying so on the survey. But in that case, you've probably already brought the problem to your head server or guest services or something.
In the 4/5 or even 3/5 case, well, I think you'll see a lot of dishonest 5/5 ratings.