Merchant gives 1 to 3 resources above its cost and nothing more, with the lower return offsetting the fact that you get to choose which resource to increase from a mixed cost.
Hidden treasure gives 3 resources, split between two rather than focusing on one, and has a condition where it could add just 1 more to each for a total of 5.
How is Oracle, which conditionally gives 6 resources after cost (or 3 in one category plus some wall or tower) worse? Numerically it's better, and by focusing on one resource, better to implement strategically. If you want a card that gives gems and maybe something extra, it is superior to both that you named. (Merchant costs more for the same effect (gems) without a chance of a bonus, Hidden treasure only gives the same gems when the condition is met with bonus recruits but doesn't exceed Oracle when its varying conditions are met.)
I'm not trying to pick a fight. The numbers just don't support your claim, and I don't see what you're getting at.
The only way I see it as being worse is if you're playing a Hidden game and Oracle is the only Far sight you have in your deck, which is simply poor design and like trying to rebalance Rock Elemental based on the possibility of it being in a deck without other Unliving cards.