I haven't really read your rules, so I won't say I know one way or the other how precise they are, but 'a tactical or situational advantage' sounds to me like it covers a lot of ground where the determinations are in the hands of one of the participants and any 2 reasonable players using those rules might commonly disagree and the resolution of their disagreement will be subjective. The EFFECT of a situational advantage may well be precisely specified, but what constitutes one may not be (again I'm speculating in the absence of having read the material, so I could be missing something there).
I think you've got the gist of the rules. I think that I
want that rule to be disagreed upon by two reasonable players.
I think what's important are the roles and authority of different players within the game. I spend a lot of text explaining how the DM's job is different from the player's job. Keeping on focus of social dynamics, I think that, in my hack, if you constantly disagree with the DM's rulings, you should find another DM. The vagueness of that rule - that it could reasonably apply (or not) in a lot of different situations - means that each DM has great freedom and responsibility to present a consistent game world. The text of my hack, explicity and over and over again, says that the DM should base his decisions on maintaining the consistency of the game world; I think that's what makes the rule clear instead of vague.
I tend to think of "reasonable" actions like the TV show Spartacus; other DMs might disagree and go with something much more realistic/gritty, and others might want more of a high-fantasy vibe. Since one of the DM's important (and explicit) jobs in my hack is to present a consistent world, I give the DM the freedom to do that. I think that's where the personal creativity - hmm, instead of creativity let's say
personal spin on the setting - comes in.
(Eero does a good job of explaining why I put that responsibility on the shoulders of the DM alone; in my hack, I want to challenge the
players, and I expect them to try and push the boundaries - but they must respect the DM's rulings, or else they are "cheating"/guilty of "misconduct"/showing poor sportsmanship. One of the player's jobs is to respect the DM's rulings.)
That's one side of things. The other side is that the vagueness of the rule allows the fiction to have an impact in resolution. I think that's important as well.
But! I'm not trying to say that this is the one true way. I wrote my hack to deliver a specific game experience, so I went with these kinds of rules. I can easily see how they would
not work given other goals.