In the Rainbow card rarity, and having a slightly higher price than the Gold Full Art version, I considered it in third place precisely because of the rarity hierarchy and because, also, Gold cards are always worth more than a Rainbow
these factors make this cards price drop an outlier
It also acts as a timed tax piece, and it covers not only the creatures exiled, but spells with flashback or unearth, spells from the command zone, casting from the top of the deck with cards like Pantlaza or Ureni
There are so many alternative arts and versions of this card that you can quickly feel less impressed when you pull a full-art
And even if you already have a few cards in hand, playing Oak at the right time will almost always change the entire complexion of your game
The possibility that any card in Historic can be retroactively rebalanced, nerfed, or fundamentally changed at any time throws Historic deck-building into volatility, and opens the otherwise static format to unanticipated changes