Texan, errors happen under any technique. Your rhetorical question presumes that the bare hand could have saved the errors you saw, but I doubt it.
The bare hand cannot be there when the ball reaches the pocket, or else the ball will strike the bare hand and bounce out.
The bare hand cannot be there when the glove closes around the ball, or else the glove won't close and the ball will come out.
The best you can do with your bare hand is clamp the mitt shut from the outside. But in those rare situations where the ball actually pops loose, you would be moving your bare hand to the spot the ball has just left. You're not likely to snare the ball that way.
If you feel better with the crutch, fine, but that doesn't mean one-handed fly catching is wrong.
Grounders are different because you will often see the ball bounce unexpectedly and hit the glove's fingers or heel, or miss the glove entirely. And the bare hand can come from above to help with that in a way it cannot with a fly ball.
I find that OF one-handed catching helps lead into the throwing motion better.