Duels Are inherently OOC they depend mainly on a players grasp of the controls, which isn't supposed to be existent. Also, an RP fight has no limits except for your imagination, which is how these RPGs got started (major tabletop DND player here) the freedom to do what you want in a combat scenario allows more challenge, more options, and ultimatley, more fun.
And RP duels to an extent rely on player acting-abilities/imagination/communication-through-narration/etc rather than be solely determined by the character in-game. Practically everything in-game is influenced by the OOC capabilities of the player to do something. -- If it wasn't the game wouldn't have controls beyond initial character creation (for example.. even with the best roleplayers.. a character's misinterpretation is almost always down to the player's misinterpretation.).
Jumping across rooftops, ascending ladders, fighting an ulbernaut, jumping across gaps of any kind... all depend on a players grasp of the controls and in many cases their reactions too... this doesn't mean they're all "inherently OOC". The way people act (or don't even RP anything prior to challenging) leading up to a PVP confrontation is, IMO... what can make the duel OOC.
As for agreeing to stand-still, if I was weak dermorian fighting a burly kran, I think I'd be more 'spritely', even trying to use cover of scenery, buildings, etc. to lose the Kran and then sneak up on the Kran from behind.
I agree that the whole running-backwards-and-forwards thing in PVP can be OOC (which I'm sure is what you're referring to Zanzibar?) and seems more like jousting... but in some cases moving around isn't OOC either, I could especially understand a weaker but more nimble character trying to out-maneuver a stronger opponent... rather than just stand there and accept their fate!
Of course, two mighty warriors, both weighed down with heavy armor... I could imagine just standing there slogging it out.
As for RP fights... they're okay when it's one-on-one, or something involving just a few people... but there are times when it's not as feasible as PVP and dependent on who is involved, it can be as futile and irritating as I know PVP is to others.
If there's a load of people involved... it can end up devolving into a rapidly scrolling chat window with people missing each others actions.
Also, if two people are too stubborn to concede to anything, you can end up with them performing stunning defensive maneuvers over and over again in a long drawn-out, and eventually tiresome RP fight... simply because they each consider their own character to be legendary. - Fortunately I don't think this is too common because the RP fights I've seen have generally been pre-determined to some degree... but you occasionally get someone who RPs themself as near-invincible for whatever reason, totally out-numbered and out-'gunned'... they act like a nuclear bomb would merely tickle them.
Of course, you could always use /roll to determine whether each action is successful or not when this happens... but that doesn't take account of your character's strength and training... unless you exchange info about your chars stats, armor, etc.
Then, like with pvp... you get irritating noobs.. who end up godmodding. --- So, as with pvp, it's worth only engaging with people that you know are going to be somewhat realistic and fair about things!!!
If it's done that way and with not too many people.. then I agree it is fun for some people... but it suffers the same potential problems that spoil pvp... in that idiocy and noobishness can spoil it too.
Really, there's a PVP system there that handles all the stats, etc. for me and is the framework in-game that represents combat... it's quick and easy to use and depends on the character-skills, training, weapons and armor. - it's also just been balanced out considerably giving everyone a better chance to win. - I'm happy to agree rules of engagement and let the system decide the rest.
To me, something that depends on your armor, weapons, skills & training, etc. is more IC than something relying on your ability to narrate your actions... it's just not performed as verbosely. But when I say it's more IC... I obviously don't mean it's as "role-playish", It just has more dependencies on the character in-game if you were to remove OOC influence.