Serendib Efreet was once a good card back when a 3/4 for three mana with flying was far from the worst thing you can be doing
The biggest contributors to this are the more interesting and distinctive support cards Wizards has been releasing in the past couple of years
It also has serious combo potential due to the massive mana reduction it accumulates
Kolaghan's change is also great, though I feel I must justify the inclusion of deathtouch: since Kolaghan is somewhat smaller than the other dragons in this set, I wanted him to be able to take those guys out
However phrased, the common takeaway is simple: a balanced platform matches clear information with fair features, letting players choose how, when, and what to playcomfortably and confidently
Dredge plays differently than a deck like reanimator that cares about putting specific cards in the graveyard, Dredge needs to keep putting cards in their graveyard for the entire game to keep the engine rolling