After playing Arenas exclusively for over 28 hours, I have come to the conclusion that Arena suck. At least keeping in mind the crappy hidden 'MMR' they have, you are left with nothing but cheap, hollow and lifeless victories against sub-par opponents. And when you do get a team that's around your skillset, the game gives you the same sub level 100 teammates that have zero clue as to what they are doing. Already said above, either a 3-0,3-1 win or 0-3, 1-3 loss.
And going back to BR, you realize that it had made you worse than you were. Ofc you will bounce back to your original skill eventually, but first few hours of BR will be just pain and suffering.
Enjoyed it for the first week but now it's back to crappy MMR. Don't play only Arena, it's not any good in its current state. I would rather get third partied into oblivion.
@xKatieRKhaosx I am not optimistic about Ranked, but I guess we will see.