The problem of Eater of Secrets was was simply that the card was complete garbage against any other deck that didn't run secrets, which was basically every other deck at the time.
Mostly looking at the Meta from Un'goro - Witchwood, up until Kobolds Hunters did not see a lot of play (let alone their secrets), Paladin Secrets also didn't see a lot of play.
Eater of Secrets was a card that was simply printed too late, it would've been amazing during the Aggro / Secret Pally Meta as the only Secret counter at the time (Kezan Mystic) stole merely a single secret from a deck that sometimes pulled out the entire christmas tree.
Playing specific Tech cards (and Eater of Secrets was certainly one of them) is always about weighing your odds, if you want to win consistently against mage, you need one, but you might lose other matches because Eater of Secrets simply sucked there.
Compare Eater of Secrets to the current "anti secret" Card, Secret Destroyer 5 Mana 4 / 6 >> 4 Mana 2/4, not the best card but at least the stats aren't total trash for it's mana cost.