If you implemented provisions into Magic, the entire community would get their pitchforks and torches out for you.Wouldn't it be reasonable to explain WHY you are having doubts of my seriousness? I mean you shouldn't just start questioning people's sincerity as a moderator without at least explaining what your reasons are.
Anyway, I believe there is a problem with what you said about 6.7% or whatever, because you have to take into account the various synergies that go along with a card as well!! What if you have two identical cards, one for Skellige and the other for SC. The card says, "If you have 3 Skellige faction cards on the field, you win the game". If that card was in SC it would have a provision costs of 0. If it was in Skellige it would have a provision cost of 1000. But it's the same card. That is a ridiculously absurd example that I'm using to just show that the exact same text is going to mean very different things depeneding on how it synergizes with other cards throughout the game's various situations.
So I'm saying Geralt: Yrden may be an 11 out of 15 in 40% of decks. But in 60% decks it may be a 15 out of 15. As opposed to every other 11 out of 15 which is an 11 out of 15 100% of the time. Again, another absurd example, not meant to throw you off, but the point is to show that there may be some synergy with Yrden that sometimes places its power level much higher than the other 11 provision cards are usually able to go.
This is why it could be useful for the provision cost to be able to reflect things such as that. How situational is Yrden? How much can it be exploited? A perfectly exploited Yrden might be drastically more powerful than its usual effectiviness level in the hands of the average player. I just think that if the provision costs numbers are too compact it becomes difficult to reflect nuances such as those.
Basically, I think ur 6.7% theory of incrimental power increases between the provision costs, falls apart across various actual gameplay situations. Like I said before, if I implemented provisions into MTG. I would give all the banned and OP cards a provision costs of 1000+. That way you could introduce formats where the deck limit was set to 500. And so all those 1000 provision cards would be unplayable. Or you could have a format of 2500 where TWO of those banned/OP cards could be used and so on. It's about context. It's not about cold hard math. What if clever use of provision costs could actually make it OKAY for CDPR to print blantantly overpowered cards? They would just have really high provision costs to make them reasonable. No card game has an allowance for INTENDED imba. But with provisions you could actually do that. Have an open mind. This is uncharted territory as far as I know.
I mean let's say they put an Exodia or something i this game. But each piece of Exodia had a provision cost of 25? Of course the game in its current state would have to have mulligan rules adjusted for something like that but THEORETICALLY. You could have very strong concepts introduced that are balanced specifically by provision costs. IT's a freedom that Hearthstone devs and MTG devs DO NOT HAVE. And you guys should be excited that CDPR came up with this concept for GWENT. I mean we could have a Dr. BOOM. We could have a mysterious challenger. Just give make them cost 35 provisions each!!
Also, considering how new the system is, I don't get how your expectations for 0-15 could have possibly solidified for any logical reason at this point.
Why do you think Magic survived this long without doing stuff like that? It doesn't need halfbaked "solutions" like the provision system, which is NOT a freedom btw, it's a restriction and if you can't see that, then I'm seriously worried for you.
Edit.: To address your idea of making the provision system more intricate: this would be a very complex and tedious process for balancing, and - and I'm sad to say this - the devs have shown in the past that they do not put much thought and effort into balancing, they mostly give +1 to cards that see "too much play" and -1 to cards that see too little. You would have to think through every possible synergy for every card and give that a number in context to every other card with all of that cards synergies...thats too much work, and impossible to get right