Gonna attempt to keep this a lot shorter than it could be, since I still don't know exactly what this thread's about.
With regards to the replies so far, this is all pretty much why I asked what they specifically were looking for comments on. Is this a discussion about how to determine who should win in a battle, or it is a discussion about how to actual write battle scenes into text (as in techniques for writing combat, as opposed to determining a winner)? It isn't actually clear in the opening post.
If it's about determining the winner of a battle, I find that stats and dice are only useful in specific circumstances, because they make battles unrealistic otherwise. For example, not all characters are created equal -- the harsh reality is that people are seldom equally gifted/talented/equipped, so using things like stats to 'balance' the characters just screams escapism, which is only fine if the role-play isn't aiming to be taken seriously. Using a dice roll to determine who would be more successful between an amateur with no combat experience and a veteran warrior is a blatant violation of realistic IC writing. Just a basic example, of course. You can't just hand wave this by giving one of them better stats than the other, because a lot of factors (not even including luck) could shift the tide of the battle strategically. I'm pretty heavy on strategy and analysis, so this sort of stuff tends to be up my alley, as Broken implied.
With this in mind, I find that using stats is only acceptable in a story that's not really going for realism (a.k.a. is taking on more of a video game logic to its battles), and dice are only a viable option when a battle situation would realistically be completely a matter of luck, which, contrary to popular belief on role-playing forums, is actually far fewer situations than people think.
When determining who should win in a battle, many things need to be factored in, including the abilities of each character, their strategic capacity, their personalities (there's a reason personality categories are so important for a CS even in a PvP role-play) and the impact their current mind state would have on the battle, et cetera. These are just a few of the factors, but ultimately trying to simplify combat with stats or dice can completely remove the very critical realism that exists in battle. In other words, to successfully determine who should win, a good amount of OOC collaboration is actually needed, as well as both participants being more focused on objectively working out a compelling result instead of just 'fighting to win' -- most good PvP role-players are more interested in seeing a deeply intricate battle be presented, rather than just fighting to try and win (it's all about storytelling and interesting strategy, but just 'picking the winner at random' does not make a good story, and neither does prioritizing winning over good writing/tactics). At the very least, that's how I feel about it. I've got quite the 'ego' on me, to be honest, but I only engage in PvP combat role-play for the intricate details of strategy and creating a compelling piece of battle fiction -- I don't need to role-play to satisfy my ego.
While you can try to discuss who would win out in advance, and in might work in certain situations, I feel that this sort of 'predetermination' takes out some very crucial elements of unpredictability. You don't really know the outcome until you start seeing the characters duke it out and the situation they get into, which is why it's better to discuss (read: discuss, not argue) the outcome as it goes, which is the very core of what good PvP is when it's not done with stats/dice. I find the only people who can't do this successfully are bad sports, such as people who rage quit in fighting games (it's hilarious how often people do this against me). If you two can actually work out who'd win in advance by factoring in all their abilities (like I said, this is more complicated than it sounds), then that works just fine. I've done it before, actually.
Honestly, I think being forced to write your posts around dice rolls is fundamentally the same as having someone god-modding your posts. The exact same thing can apply if a winner is chosen in advance and then you have to write your character OOC to achieve this 'plot-induced stupidity'. That's why I think being able to maturely discuss these sorts of things out is what determines someone's ability to write a compelling battle scene with another writer.
This is, of course, all assuming that the discussion is about determining a winner, instead of techniques for actually writing fight scenes from a literary point of view. I'll provide another response if it's about the latter, because I can help with that too. I wanted to wait until I knew for sure, but since other people responded I figured I'd throw my two cents in.