You'll be missing a bunch of good cards in both decks. Can you still be competitive? Depends on your meta, really. Personally, I find the Farstrider expansion more valuable. The dwarfs give you Precise Use of Force, Earthquake, Fuelled by Fury, Ready for Action, Trap, Light Armour, Shifting Image, and Shadeglass Axe, as well as Second-in-Command if you plan to buy the Leader pack, but the Farstriders give you Advancing Strike, Change of Tactics, Defensive Strike, Heroes All, Great Concussion, Improvisation, Inspiration Strikes, Quick Thinker, Shardgale, Spectral Wings, Twist the Knife, A Destiny to Meet, Concealed Weapon, and Incredible Strength. That list of just full of win.
Can you be competitive without those cards? Sure, but not as competitive as you can be if you have them.