I tend to think that Diana's mission is specific despite being far-reaching; not just "spreading peace and love" or "hunting down magical threats" but something that isn't so vague or open-ended.
She's sent to Man's World to spread the Amazon philosophy. She's here to save us from ourselves, and will prove through her actions and arguments that the Amazon way is superior and worthy of adopting on a global scale. She's got a clear goal with clear objectives, which helps set her apart from her peers, most of whom are engaged in a nebulous never ending battle, who have no real plan or goals beyond the hope that their actions somehow inspire others to be better people (and they rarely define what that even means, as well).
Now, doing stuff like removing Ares' influence from man, yeah that's all great as far as being part of how Diana will achieve her mission, but I don't think that's the end game; it's just a step along the way.
It's a political motivation, and one that I don't think can actually be achieved. The whole world isn't going to embrace the Amazon way of life no matter how heroic Diana is, how well she argues the merits of her philosophy, or how many Crisis events she stops. I mean, "submitting to a loving authority" isn't something I'm willing to do, personally. The closest I come is ensuring my wife is happy and satisfied and has what she needs and wants. But I'll burn before I trust a politician any further than I can physically throw them. And I suspect more people around the world would agree with me than with Diana on this.
I think this adds a lot to Diana's narrative. Once she's around for a bit, she'd start to realize that her mission isn't going to be accomplished easily, if it can be accomplished at all, and she may find that certain aspects of Man's World are just as good, perhaps even better, than her own culture's. I mean, ice cream am I right? Yeah, there's plenty of great stuff from the Amazon philosophy all of us *should* try to emulate, but adopt it completely? Probably not. So there's inner conflict to play with; Diana's trying to fulfill a mission she's honor bound to accomplish, but she knows it's impossible and maybe doesn't even want to see it done completely (though she'd recognize that we could do with adopting at least parts of her philosophy). It provides conflict with the Amazons and the gods, as they get impatient and bitch about Diana not getting the job done fast enough, perhaps wondering if she was the wrong choice for the role. Not to mention various governments who might consider Diana trying to "convert" the population borderline treason. And it makes Wonder Woman more unique among her peers; while Barry Allen is just hoping he somehow makes Central City a nicer place, Diana is writing books, making public appearances, and pushing/supporting political policy.