That's where professionalism comes in. My hobby is climbing and cutting trees. Everything has a place on my saddle, and my gear is clearly differentiated. If I do the wrong thing at the wrong time, I'm gonna have a *really* bad day.
There should be no way someone of even below average intelligence, much less a trainer, can confuse a pistol with a taser. You do what it takes to not confuse them, and train. I'm not in the business, and just watching from the sidelines, but /I'd/ have the taser on one side of my body, and the pistol on the other. Even under stress, if you're grabbing from the wrong side of the body, alarm bells should be going off.
In any case, if any one of us did something similar, we'd have gotten a similar sentence. Being a cop doesn't give you more rights than anyone else, and the responsibilities are greater. That's why they get paid.