That's a horrible approximation: Mario is weight value 98, Pikachu is 79 -- it's a gap the size of nearly half the cast. Pikachu is not "heavy enough to be comboed" either. Duck Hunt is weight value 91, the weight of Palutena (who, hint, is pretty hard to combo,
unless HH was missing some magic strings here).
DHD's Fsmash hitboxes end on frame 30, then he has 37 frames of endlag. What you are advocating is after that hitbox is over, roll from the ledge, which takes approximately 48 frames, then do a smash attack, the fastest of which is Dsmash, first hitbox of which comes out frame 9. A normal roll behind takes 31 frames by the way, same thing. Fsmashes first hitbox is frame 15, good luck with hitting that.
For the love of God, keep using bombs, in this MU too. But you know Drizzy wasn't even asking for critique, generally people just ask if they want input.