I did some testing though and explosive rounds arent THAT great if you are good at precision shots.
For instance against the same type of enemy, a precision hit with my Mida would do 300 damage. A precision hit with my nameless midnight knly did 200, and the explosion did 80. So that is less damage. The explosion hits nearby enemies too, but they have to be EXTREMELY close. You would be lucky to have it damage 2 or 3 enemies tops if they are tightly packed. So Mida > Nameless Midnight IMO in almost every conceivable situation, unless you are really bad at scoring crits. Even the I think Mida does more dmg with body shots too.
Handcannons on the other hand, probably wont precision hit quite as much, so tbe explosive effect helps out more than with scout rifles.
Also even with lower impact, exotics seem to hit harder than a same class weapon wirh higher impact that is only lgendary, if the impact isn't too mich higher.