User blog comment:LilyheartsLightning/Citadel and Reckoning DLC announced/@comment-1440333-20130225225803/@comment-4953843-20130228152206

rebellion: ~130 MB

earth: ~180 MB

reckoning: ~200 MB

resurgence: ~210 MB

retaliation: ~410 MB

a quick googling should back these up if you haven't really downloaded them.

thought you're right that there's fewer content in reckoning that hasn't been seen before since most of them are just repurposed from existing assets. then again most of the other multiplayer assets are.