I reckon they'll release more 4* flyers with class buffs in the future to make them more accessible, maybe even as GHB units. Although Valter isn't coming with any, shame.
Edit: Also, for anyone looking to farm items in Arena assault, if you enter your first match with a single lvl 40 unit and choose the easiest match, you'll fight a 1v1 and the other 6 beginner matches will also only have 1 enemy unit at lvl 40, which is enough to get you an easy 7-streak for 3 items.