I think most people do it because with braid you can get away with running a substantially stronger line with no increase in overall diameter compared to an equally rated mono and minimal increases compared to lighter rated braids.
For instance 10 lb mono is typically 0.012" in diameter vs 30lb mono which is 0.022"
On the other hand Braid in 10 lb is .006" and 30 lb is .011" and 65lb braid is just .016'!
With that said, equally rated braid will always be thinner than mono so if you can run an equal amount of line that is twice the strength, the answer should be obvious. I understand your point on "overkill" but some people would debate a 12in bait is overkill yet we keep on chucking them.
I personally don't like to run braid however I have snagged a hudd or two in my day and having 65lb braid vs 30lb mono very well could have made the difference in getting it back.
just food for thought.