While Elite Barbarians may be labeled as leveled up Barbarians, the faster movement speed they possess could be a significant difference that allows Elite Barbarians to stand out from regular Barbarians.
Supercell has their way of making ideas work. For example, take the Bomb Tower. They had to add in a new mechanic so it wasn't obsoleted by the Wizard Tower in terms of range and damage as well as coverage for air, and that was the death damage.
Sure, the Bomb Tower may be faster than the Wizard Tower in attacking but it isn't much and the DPS is lower anyways.
Now for them to find a way to make other Clash Royale troops work.