BGs should not be larger then 10v10. Honestly 8v8s with objectives and an intimate map that is not oversized is ideal. That player count with proper maps allows for player agency and places a measurable responsibility on every player involved. The larger you get with stupid objective gimmicks and oversized maps, the more you allow non contributors rewards. Think wows isle of conquest (garbage) vs swtors hutball (or any warzone honestly).

Small scale bgs with lean objectives, fostering player responsibility

A good battle ground is one where a single player is afforded the possibility of a game saving play. Each player needs to have the same percent chance to effect the outcome of a match. Do not confuse this with thinking "team work takes a back seat?". Absolutely not what i am saying. Think dota (not LoL because lets not be plebs thx).

As was mentioned earlier here, arenas should not be 4v4 under any circumstances. At least not if they are to yeild tangible rewards. You come as close as you possibly can to balancing combinations of builds or classes in 3v3, and everything else begins to fall into place more or less. There is plenty of nonsense in cyrodil atm that would laughably get exposed in a focused 3v3 environment.

But with that being said, and i know this will be a VERY unpopular opinion.... I feel break free should have its resource cost removed and put onto its own cooldown. Otherwise you will never acheive a competitive arena environment.