This one is on me as I was running Feed at the time. But, as your tweet points out but your headline not, we valued all reactions higher than likes, because it’s a stronger signal intent. It’s the same reason why we value comments more than likes.
As you point out in your fifth paragraph, we learned and iterated as we always do. Also worth noting that, if my memory serves me right, the order of how popular each reaction was was strictly the order they appear in the UI, and the angry reaction is last.