EDIT: Analysis of Skink Chiefs, not Skink Braves! (My mistake)
They seem quite useless on foot, yes. The leadership they provide a skink unit is a waste, as skink units are sacrificial anyway. A skink unit shouldn't get into combat (or at least, its not their optimal use), so that extra leadership and higher BS on 2 shots is really everything you gain by taking a skink chief.
In my eyes, skink chiefs are good for 3 things:
1. Using his BS 5 to get the giant bow on a stegadon more accurate.
2. Equipping him with the Stegadon War Spear and mounting him on a Stegadon Ancient.
3. Equipping him with Staff of the Lost Sun. With 3x S5 shots per turn firing on BS5, he might actually be useful on foot. In that case, move him into a wood along with some blowpipe-skinks and fire away!