I know we have a similar discussions on other threads but I still thought its worty of noting the balance difference. After the recent patch arena rewards became even less good, Here is my 9 battle PVP earnings and my rewards for completing the arena. Granted on PVP I played with Valkyrie/Alchemist and on warlord I difficulty while on arena had no Valkyrie and played on normal difficulty but again its worth mentioning that on PVP you can play on higher difficulties because you have a better set up team while on arena you might end up playing with a rather poor team which would be rather suicidal to play on higher difficulties than hard.
9 PVP battles gave me
18,998 gold and 412 souls.
After completing the arena (in 9 battles) I got
3,421 gold and 302 souls.
So I got 5 x times more gold and around 100 more souls while playing on PVP. Yes I was using Valkyrie but as I said - PVP is about your own team set up which allows you to do some farming.
Seeing the results makes you wonder why would one still play arena? 3 Glory keys in my opinion are worse than 2 Iron keys used to be and with lesser soul gain its kind of tough to see the point in arena battles.