That's the tradeoff with m43 to begin with. F2.8 is f2.8 in terms of light gathering and low light shooting, but in terms of DOF, it like f5.6 on a full frame. Just as the Pany 25 f1.4 is like f2.8 on a full frame, etc. In terms of shallow DOF, this is not the same as a full frame 24-70 f2.8, but for shooting weddings or other low-ish light events where you need a zoom, it's the first m43 zoom to get you there.
I think it's as reasonable a comparison as comparing ANY m43 lens to a FF "equivalent". They're all equal in some ways and not in others. That's a given.
-Ray