I thought the Soul Stealer perk just recharged your current weapon, instead of being "Soul Trap On Hit".
You can either Soul Trap something to fill a Soul Gem, or let Soul Stealer just keep your weapon fed in combat.
I think the one you are thinking of is Soul Squeezer. No wait that makes you get more magicka out of soul gems... I know which one you are talking about though.
And if you don't like it you don't have to get it. It will be fine if let's say, Azura's Star returns. Or you keep plenty of small soul gems on you.