Fair, but in the long run i think there needs to be something more than just banes to impose a challenge. While you can "stack" banes to make it harder to nullify, it risks becoming "samey".I agree with your opinion on Opposed Rolls, but please, no penalties! Dragonbane made a good decision to cut modifiers completely and to just use boons and banes. If you are starting as you suggested, it won't take long until the first person demands a table for ranged combat modifiers. If you do something that would pose a challenge, you get a bane or two. Done.Now there should still be a mechanic to make a situation harder, and i would for that pitch this: Challenge rolls.
The core idea is when you do something that would pose a challenge, the gm can declair it a challenging roll. This gives the player a skill level penalty for the roll, reducing it by a certain amount of levels depending on the challenge. These should be fixed values, so the player knows exactly how much to reduce (the following are just examples, values could be different)
Lesser challenge -3 (-15% chance of success)
Greater challenge -5 (-25%)
Imposing challenge -7(-35%).
While i disslike opposed rolls as written, it at least makes some vararity, and you can crank up the difficulty (an opposed roll and a bane are bad. A opposed roll WITH a bane is a rare "oh shit" moment, but makes it all the more cool if you defy the odds and succeed)