I have given consideration to those downsides. But the impact of those downsides is minimal or negligible in terms of downgrading my evaluation of the card. We know exactly what the downsides are because they're essentially the exact same "downsides" that existed for a Mage that ran Mad Scientists. You have to put secrets in your deck. You might draw your secrets before you draw your minion. We've been here before. And we know from Mad Scientist that the downsides are tiny. In fact, there might actually be FEWER downsides to Arcanologist. If you do draw it late, it has better stats than Mad Scientist. Also unlike Mad Scientist, the effect can't be blocked if the only secret in your deck is exactly the same as the secret you might already have in play.
Now, I'm not saying that Arcanologist is better than Mad Scientist (there's probably only one card in the game that is) but I am saying that we should know from experience how powerful a card like this is in the game of Hearthstone, and all of that past experience should tell us it is OP.