This is an interesting topic. Dungeon of Forgotten Heros (DoFH) was a MOBA (Multiplayer Online Battling Arena) based battlefield. It had the same mechanics applied to this game. Players would pick one of the heroes/champions/characters they liked and played with it and just like in MOBA games, the characters had certain characteristics to them. One of them was a healer who would resurrect others when they had lost soul effect, heal them in fights, basically take the support role inside, another one would use mirror on others, focus on taking the enemies down fast which made it an assassin character, another one would be very tough and focused on killing the PvE monsters inside the battlefield and collecting currency to buy items (it's called farming minions) and so on.
The battlefield worked like this: Players would queue up for it, when it reached a certain amount of players in each side, they would get called inside the battlefield. Inside, they would have nothing on them, all of their belongings left behind and would be inside a shop with a number of incarnation elixirs all of which are sold for 1 gold. They would be able to buy only 1 of them, use it and start playing. The main goal inside was to destoy the enemy nexus (their source source of energy inside their base). If the nexus of team 1 was destroyed, team 2 would win and vice versa. The winning team would gain a good amount of valor and 20 reputation. The losing team wouldn't get any valor and would lose 10 reputation of that battlefield.
The problems start with the tactics themselves. There's no certain tactic because players don't get to or choose to talk about what they will do. Every team needs a certain amount of assassins who will attack enemy team's farming players, a certain amount of supports and a certain amount of farming players. But it usually ends up as miscommunicated team and everyone tries to do what they know best instead of playing as a team. The whole battlefield is built upon teamwork. Just 1 player not co-operating could probably cause the whole team to lose the game. At this point, best tactic to do would be starting to communicate with the rest, everyone choosing the best character they play as and giving it their best shot. Protecting the farming characters, killing enemy farming characters and making sure the farming players would reach enemy nexus and finish it off.
I personally would fix a lot of things with the battlefield. The class differences are too high which should not happen in a MOBA game or a MOBA battlefield. Of course there are certain Meta characters, every once in a while some of them get stronger, some of them get weaker, some of them stay the same. It'd be best to let the player be the deciding factor in the battlefield, not the characters themselves. It shouldn't be too easy for an assassin to let's say kill a farming player. Or the item prices, they are too high and it's too hard to kill the minions. For starters, everyone would be able to farm, minions would take 15 seconds tops to kill instead of a minute or two. That way everyone would be able to farm, get their items and start doing work. A level-up based character system is what I would implement, everyone starts with 1 skill, every time they level up, they start opening up another skill and at a certain level, their most valuable skill/ultimate skill would be open. Maybe in the future, it could be possible for characters to let's say reach level 15 in time and upgrade their already existing skills, therefore having a better chance at dominating the enemy since they'll be higher level and have a better skillset against the enemy if they know what they're doing.
I'd add ranked/competitive queue and a normal queue. Normal queue would be for fun, everyone would get valor and just beat each other to death inside, but ranked queue would be where they get both valor and reputation if they win, if they lost, they'd get nothing and lose their reputation (just like how the battlefield used to be).
Last, but not least, I'd add dynamic changes into the battlefield. For example: Arboslam (which is a farming character) has x amount of seconds/moves cooldown on its first skill, it'd be lowered into x-2 moves which would make it a more viable character compared to others. Therefore making him meta, after a month or two, make some more changes, his move becomes x+1 cooldown, but troll would get a y-3 cooldown on its let's say 2nd skill. What I'm getting here is balancing everything with a buff-nerf system and making players choose different characters every few months, doing the same to items, let's say an item has 50 physical damage increase, I'd lower it to 40 next update, and increase something to 60 in another... Making the battlefield feel more like a MOBA. Of course, all of these could be tried out and if they don't work, they wouldn't be implemented.