You thought wrong. Characters who can use powers meet the prerequisites for feats, but they are never considered to possess those powers.

However, going the Mercenary route complicates things a bit further. Since the Mercenary can only use the TA when he's adjacent to a more expensive Superman Enemy (who'd then get the outwit himself!) your Mercenary would have to be adjacent to both a more expensive Superman Enemy AND a less expensive one (or a less expensive Wildcard) to get the benefit if double outwit himself

Where can this ruling be found?

Lots of places. I'll let you do the search. (I'd try looking for "Harpua Leader" in posts by nbperp to find confirmation.) It started with HSS and the Sentinel of the Skyways. If you begin an action using regular HSS and get a crit miss or Mystics to drop into the SP HSS, you have a new power and must stop.