As others have said, arcane is decent when specced for aoe. Just be aware that if you take the aoe talents and traits, your boss dps will be significantly (READ: about 40%+) reduced which will really show on tyrannical weeks.
That’s pretty much the crux of the spec’s issue right now: you can do st or aoe but not both. If you try and split it, you’ll be gimped at both. I’ve started running frost in mythic+ and keeping arcane in raids, but here’s hoping that in 9.0 the spec is redone.