Butterfly bars give you more hand positions and a little more stretch, or a lot less stretch, depending on how you deploy them. A shorter more upright posture is not more comfortable, certainly a huge disadvantage if the wind ever blows. The main disadvantage of butterflies and flats is the same: not as natural a position for the hands, and your medium position isn't on the brakes. On drops you have 2-3 basics positions that are more ergo, more aero, and on the brakes. Wandering around on the road with triathlon type extensions as though you were on a closed course does not give you the safety of drops with fingertip brakes. And in the example shown above you would be trading the brakeless stretch for a position still about the same as granny on you shopping bike.
The only really bad part about drops is getting a working brake combo, and the STI situation. But you can use bar ends which is at least one position on the brakes and the gears, and your average position is no further off the gears than the butterfly bar. STI has a pupose but it isn't necesarry for everyday use. It's certainly fun.
Flat bars are comfortable for a short ride, but for long rides, I don't enjoy them, if you feel otherwise that's a big factor in their favour.