So many people can't read. The card description does not say "Return all monsters on the field to their owners' hands". It says "return CONTROL", so no shit the opponent needs to control your monster first; otherwise why would you need to use this card? Lol.
the first word on the card description is RETURN.
RETURN - verb (used without object)
to go or COME BACK, as to a former place, position, or state.
So if it has to come back, you have to lose it in the first place. So yeah, there's your lesson.
This card can be very useful in combination with mystic box. For example when you encounter suijin, you can summon a weaker monster, then use mystic box to destroy suijin. Activate owners seal to regain control of your monster, then you can enter battle Fase.