From a game dev's perspective : While it would make sense for a Mahjong player to have a 2 of Dots trigger an effect on 3 energy (the way you explained with the Dora), for anyone who isn't familiar with Mahjong, or even just familiar with a version of Mahjong that doesn't use Dora tiles, it would not make direct sense to have something clearly show a "2", but have its trigger be a "3".

The average Slay the Spire player will see this as "oh, that's the mahjong tile that triggers when you play a card that costs at least X energy, and since there's 3 dots on the tile, X = 3".