The ESA is a very real thing. The only difference between ESA and SA is that a SA has some kind of specialized training to perform a physical related action for it's owner. (Leading them, barking if someone is at the door, etc.)
Yeah... all dogs bark when someone is at the door.... go figure.
An ESA fulfills a psychological role. That may prevent anxiety attacks, depression, emotional impulses and triggers. There are plenty of both kinds down here. I've even done gigs on some long cruises where there have been both kinds. The SA are generally more well behaved and reserved. The ESA tend to be "children" if that makes sense. On one cruise, there was a beagle that it's owner would actually dress up in little clothes and push around in a baby stroller. Even wheeled that little dog up to her dinner table and placed it in a booster chair.