Dewbacks have more health, do more damage, move faster, and take less troop space than Heavies. Not to mention opening the walls for other troops and having splash damage. They were literally my go-to unit from hq4 to hq6. 12 to 15 Dewbacks, maybe a bike or 2, and the rest Stormies and I got 3 stars at least 9/10 attacks, usually against higher bases.
The caveats are that they can get wrecked by traps if too many are clustered, and they're weak to mortars. Just stick to bases that aren't mortar-heavy, place them so as to hit mortars early, and spread the the deployment so they won't all run across a single trap, maybe use a few Stormies to trigger traps until you get Shocks. A bomber to clear traps is another option, though I never used it.
Really your only worries should be hitting a trap with them all clustered or SC troops