Since I do not own the card, I cannot tell for sure if it can steal anything, but my opponent kept stealing my 10+ power creatures with this card. Note that these creatures were reinforced and under 6 power when not reinforced.
Are You sure that it’s the Welcome to the Fold spell is cast?
Maybe it’s the Exert Influence that opponent casts?
That would make a big difference.
Jace1 can also lower the power of creatures with his first ability, allowing it to combo nicely with Welcome to the Fold.
I am absolutely sure it was Welcome to the Fold and also sure it did not affect the power of my creatures.