Ad Sion is ok but the passive could do with a small nerf early and adjusting so it doesnt do 0 dmg lategame. Tank sion is trash because tanks other than Tahm are unplayable top, even Nautilus. Sion Q is nerfed hard in the early levels, look at a fully charged Q rank 1 and it does mediocre damage.
Vladimir Q auto does more damage that a fully charged Q and the Sion Q is hard too fully charge unless from a bush. Another issue is you can flash out of channeled Sion autos 95% of the time.