In interactions between a professional and a client there need to be firm boundaries. That is especially true if physical contact is a normal part of the interaction. Doctors, massage therapists, personal trainers, physical therapists, nurses... they should be able to expect that they will be respected.
I guarantee you that everyone who works in these professions has had at least one client who tried to violate those boundaries in a sexual manner. They would be rebuffed and the client would not be seen again.
Imagine if a big beefy dude were giving you a massage for back pain and he suddenly started massaging your balls. Then you find out that a dozen other men who have gone to that massage therapist have had that happen.
In this case its 23 women, and Watson is a big beefy dude who could easily overpower them. Its the fact that he does this over and over again to unsuspecting women which makes it egregious. Like it or not, being an NFL quarterback makes you a public figure.
He destroyed his own reputation and a short ban is not going to get it back. He should have been banned from the sport.