I think an initial investment into cards on top of the spell book is required if you don't want to struggle. With just the starting card, you will have a tough time winning fights.
I totally agree with you here. It's definitely necessary to invest a bit. It's almost impossible to grow organically out of novice league because you get so little rewards there. If you are in silver or gold, it's much easier to grow with the rewards only.
!ENGAGE 20