Soul boosts are bad?

Hi guys, I'm just wondering if I'm missing something about the soul boosts. I was bought one for the poison path because the poison kept on killing me. However, for this boost, whenever the poison fails to apply to your champ, which is every 7 seconds, the defender gets a 7 second unstoppable buff. So that means that if you don't have a champ like Cap IW the defender stays unstoppable for the whole fight! How are you supposed to defeat them if you can't even hit them. Maybe I'm missing something so correct me if I'm wrong. Thanks all!
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Comments
She hulk as well but she's poison immune anyway.
If its a buff then champs like Sym Supreme should be able to nullify too.