Shiki tries to lift something and Fujitora increases the gravity, they would just crush everything. But Fujitora can also descrease the gravity and don't need to touch something first, to be able to use his DF on it like shiki does. Fujitora's DF > Shikis.
Yes if Shiki wants something to go up and Fuji go down the thing will likely crumble I agree with you.
But I don't think the power of Shiki is inferior : if Shiki touchs the ground he has a lot of possibilities that can bother Fuji. Shiki powers if he touches water he can create a lot of things with water etc while Fuji can only be more brutal with his power.
Shiki real weakness is that he has to touch things first. But I think his gravity power are more versatile.
So I don't think Shiki df is weaker