I started a new account, to help one of my friends start playing, and when we got 500 score for the first rare, we were stuck grinding AI 3, before the arena was implemented; we'd still have a fair chance at winning Top50, and spinning rares even if it wasn't from a farm. Now we have arena, the easiest of them Bronze is harder than Top50 was. With only one rare, which may have been a poor choice, I'm finding it hard get a deck for new players which can beat anything higher than AI3 (unupgraded, one rare). The Bronze win rateis less than 50%, and the rare spin rate is much lower because of it. Our best shot is 6 wins in a row, and with less than 50% for one win, doesn't look like it will happen.
The only thing I can think of that won't imbalance it, but still makes it easier is to not allow bronze decks to spend points in upgraded cards, so the only advantageBronze decks have over new players' decks is the hit points.
I'm sure there's many people who don't agree with any of this, but it's late and I may have not made it sound the way it should.