Really? I find Iceborn Gauntlet to be a hugely affective item on Sion. It locks opponents in place long enough for you to get Qs off as long as they don't have a dash, keeps them in range for W, and between Q, E, Randuin's, Exhaust, and Iceborn (and Furor), I find it really easy to keep enemies locked down long enough for my ADC to clean house. Not to mention Iceborn gives a huge 125% bonus base AD steroid to Sion's basic attack (and Sion's base AD is really high).
The AP also helps with Sion's E's damage, which I use a LOT.
But if you don't like it then that's fine by me.