You might also say that both those cards are underpowered since with 30 bricks you can also get 84 wall with Hidden Traps. In general, low cost cards are more efficient than high cost cards (I think for the simple fact that a turn is a valuable commodity).
The exception comes with some of the highest cost cards in the game (notably Gateway, Orc Regiment, Dragon Squadron, and perhaps Curse), where the scales tip back in their favor, and they are more efficient than their mid-cost counterparts, but Fortification isn't quite high cost enough to justify that.
Another thing is that Dwarven Fortification is a keyword card. Even if someone might not use it otherwise, it could probably find use in an Alliance-themed deck (even if they're not going to use it a lot), since Alliance has an excellent side effect, so just having it sit in your hand will be useful.
All that said, it could probably still use a little buff IMO. It's not hideously underpowered though.