I have also seen a number of attempts at explicitly defining this, not just for 40K, but for competitions in general. The one I like best is that a given contest is Competitive to the extent that Player Skill matters above any other factors. Even with that established, tho, we've still got a lot of uncovered ground. Which Skills do we want Players to be pitting against each other? What are potential "other factors"? How can we measure the ratio between the Skills we want to compete at and those other factors? And finally, the bit that generates all the controversy, how can we tell whether given modifications of a system (i.e. Tournament Comp/Rules Changes) make it more or less Competitive?
40K is complex enough that we don't have nearly enough data to quantify exactly where it falls, but it's clearly somewhere between the two extremes. We see the same Players consistently showing up near the top of the various Major Tournaments time and again, so it can't be purely random, but there certainly are random factors, and they can be game-deciding, either because someone hits the far end of the bell curve, one way or the other, or because the Players are so closely matched that it ends up coming down to one dice roll.
The role of randomness in games is actually pretty fascinating, and a very complex topic. I've got another post planned just digging in to that.
Even in those Games devoid of randomness, tho, there is variation in the level of skill involved. Tic-Tac-Toe is simple enough that even children can completely solve it, working out that in any given situation there is an optimal play, and whoever goes second can always force a draw. The others I mentioned become progressively more complex, with Checkers having been completely solved by computers, Chess not completely solved yet, but sufficiently understood that the best computers can always beat the best human players, and Go still at the point where top human players reliably beat the best computers.
I want to single out Go here, for a second. Not only is it so complex that computers aren't yet able to play it at top levels, but in a different way, it's so well understood, and so clearly skill-dependent, that new players can be ranked fairly accurately after just a handful of games with players of known ranking, and modifications can be applied to allow players of quite widely varying skill to play a roughly even game.
There are other factors as well. Some are within the system itself. Most notably, a clear and unambiguous rules set like War Machine is more competitive than one like 40K where many points are poorly defined. I've seen people lose games at major Tournaments because of unclear rules that were interpreted one way in their usual environment, and another in the environment that the rules judge came from. Winning a game because of poor writing on the part of those who created the game says nothing about a Player's ability to compete. It is, at best, a random factor, and at worst, an opportunity for cheaters.
Then there are balance issues. No game so complex as the wargames we play can be 100% balanced, but there are degrees, and when the balance is so bad that some Factions/Units are obviously vastly better than others, the skill required for List-Writing goes way down, because the viable choices are so reduced, similar to how Tic-Tac-Toe requires less skill than Checkers, because there are so many fewer options.
Unlike traditional Games, wargames often feature a variety of Missions or Scenarios which can lead to further balance problems. 6th Ed 40K was dominated by gunline Armies because the Rules for the Scenarios had Players placing Objectives after knowing which side of the Board they'd be on, and allowed them to place the Objectives further back in their own territory than 5th had.
Balance is also an issue because a poorly balanced Game allows for fewer Playstyles, and thus there is less that a Player has to prepare to face. If you know that only gunlines are going to give you serious opposition, you optimize your own gunline to take on other gunlines, and just stomp all over everything else. If you're also getting viable opposition from Assault Armies, glass hammer Alpha Strikes, Null Deployment, and Armies that focus on high durability and Objective-claiming power, optimizing your list becomes a much more difficult affair.
For instance: we're all drawn to the Game by different things, and it sucks to see someone who has impeccable skills all but entirely shut out of competition because they can't stand playing Eldar, or can't afford a whole new Army every couple of years any more. New releases shaking things up is good, and it should be important to vary lists as the Game evolves, but Player vs. Wallet isn't a Skill we're ideally looking to test here.
The fact that we need to get through competitive events in a reasonable amount of time is another. There is some evidence that super-horde Armies with Model Counts in the 150-200 range can actually be really good in 7th Ed, but you don't see them gaining much success in Tournaments, because few Players are capable of finishing Games in a reasonable time limit with that many Models to deal with.
Until next time, y'all have a good one, y'hear!