Which one fits best in arena? From what I understand multi attack is 50% dmg, while extra attack is full dmg? What is the chance för extra attack to go off? Any point in using both?
Also what is the cap on multi and extra attack in arena?
The legendary multi affix don’t seem to scale down, so still +2 in arena, is this intended?
Would just like it if someone knowledgable could talk about these two and explain pros and cons etc.
Thanks 
Multi attack is 100% chance of multi attack for 50% dmg. EAC = 50% chance to an extra attack to do 100% dmg. You can use both and they will work together. MA caps at +2 in arena, not sure about outside, although I know +4 works. EAC also caps at +2 in arena.
MA and EAC also effect all of your skills: If you use a flintlock, MA will effect Scatter Shot along with ricochet. Depends on your build for pros and cons.
Multi is better
Extra atk chance have a low rate at arena
MA and EAC also effect all of your skills
I think MA only works for some skills ? For example: I cast Meteor with +2 MA then I only see one Meteor hit the ground
Only primary are affected of MA like bow gun for meteor upgrade it to 20 and see want happens
What he said ^. Sorry, I get caught up in my mind sometimes. 
or better yet build it to 40 with items haha. i love how my wiz becomes skyfall itself because i have like 6 meteors in one cast haha
Yeah 40 is better haha
i might try a build with that. my current build is a super weak aftermath which will take me about…forever to improve