don't forget that every single time a province finishes scouting, the cost and difficulty for every unscouted province goes up a little bit. While late-game players will almost never see a change, the early-game players definitely will. And will end up with red provinces that are very tough to complete. This penalty from overscouting is very real.
Again if you get anywhere, anywhere near the orc wall. you are already a negotiator. cost and difficulty at that point are moot and pointless.
Because you negotiate because you have plenty spare goods (It's very easy to produce more goods than you need for the tech tree / upgrades)
The further you get in the game the bigger your pile of goods usually becomes, only the spire can be a real goods drain (or way to expensive tournament provinces)
So if you battle provinces, you'll never can make it too difficult since you simply cannot scout to far away. because once that happens your battles become to difficult and you have to way for another squad upgrade to unlock the provinces.
If you negotiate you have spare goods, this is where you can scout many rings ahead of the tech tree. at this point you can spare the goods anyway otherwise you would not be at that point. that you might spend a million more goods by the time you reached ring 11 doesn't matter. you have those goods to waste anyway.
We are talking about halfway ring 9 (160 provinces to unlock orcs) vs ring 11 (223-264 provinces)
That means a negotator can scout up to 64% more provinces than a combatteer.
As for long term things, My dragon abbey would have been producing only 2/3rds of the mana if I was a combatteer vs a negotiator.
There are tangable befenits for negotiating as many provinces as possible. even if it looks pointless.
Several productions / effects have a "times completed provinces" component. so if you hold yourself back you actually hurt yourself.