Arena is so easy!
You people are just unskilled at Arena.
Here is a set up which you can aim for:
THE CLASSICAL ARENA SPEED NUKING SET UP
Leader: Speed Aura
1st move: Turn Meter Filler + Speed Buff
2nd move: Increase Attack
3rd move: Decrease Enemy Defense
4th move: AOE Damage Dealing [Damage Scales Off Attack]
^^^^^ All can be done with heroes you acquire from Campaign.
Leader: Spirithost - Speed Aura 10%
1st move: Diabolist -------------> Turn Meter Filling
2nd move: Spirithost ------------> Increase Attack
3rd move: Warmaiden ----------> Decrease Enemy Defense
4th move: Starter ----------------> AOE Damage Dealer
When you reach 30 day login, You will acquire High Khatun
High Khatun is better vs. Diabolist
High Khatun will replace Diabolist
Leader: High Khatun - Speed Aura 19%
1st move: High Khatun -------------> Turn Meter Filling
2nd move: Spirithost ----------------> Increase Attack
3rd move: Warmaiden --------------> Decrease Enemy Defense
4th move: Starter -------------------> AOE Damage Dealer
If you pull Bellower from a Shard, You can use Bellower in place of Warmaiden.
Bellower can do Decrease Enemy Defense.
If you pull Apothecary from a Shard, You can use Apothecary in place of Diabolist.
Apothecary can do Turn Meter Filling
You are facing level 60 teams in Bronze because those teams are bad!
If those teams were good, They would be in Gold!
The only reason you are losing is because your team is bad + under leveled vs. there bad + max leveled team.
When your team is very good, You can beat them even if some of your heroes are under leveled.
The main heroes which you need max leveled are your damage dealers which is what Betel already explained on this forum.