sounds cool.
why does it have to be vistani transporting you though?
Hai dere, you must be new to Ravenloft /sarcasm. Attempting to travel between the mist bordered domains without prior knowledge and preparation is incredibly foolhardy. Most seek the Vistani because they will allow anyone minding their manners passage through the mists with them for recompense. Only the Vistani and certain Ezrites know how to navigate the mists without the chance of wandering off into the arse end of nowhere. The Ezrite faith is seen as insular and occult by very many of Ravenloft's natives and so the lesser of two evils, the mystical Vistani is often chosen.
uhm, actually you are wrong on a few facts.
First the Core has relativel stablity between the borders of the various domains. If you theory was true, then trade would not exist period. But yet that is not true. barovia is a major trade route between the west and east due to the mountians making it the only stable route. Further more in the west their is often various diplomacy and connections. Yes Darklords can raise misty borders but this is a rare used ablity, and not a common sight in the Mists. This is also not counting the wars of Falkovinia and drakov which i guess according to your views means that falkovinians also have mist traveling powers? except that is wrong. The Core is relatively stable in terms of mistyness
Now on the other hand, clusters not part of the core; which btw Har'kair is one of them. In Clusters this is how you say it is sort of as there are 3 ways to get to a cluster. 1.) ezrite's divine will through Ezra. 2.) the mysterious Vardo. 3.) take a mist route, can't remember the exact name and hope for the best. Some of these are far more stable with similar stablity to the core as core mists are then others which are unreliable as hell.
Finally on regards to the ezrites, you are plain wrong. Unless you regard the following lands as insular: dementlieu, mordent, darkon, borca, richemulet, and Invida. Which btw are not insular domain at all. Those domians are also all pretty much wholely ezrite religious lands, even if other faiths exist, the exception is Darkon which has the rapidly expanding fourth sect in that area and only has a significant portion((which is still large considering Darkon's size)). The church of Ezra is an -expanisonist- religion. They want to expand and bring the faith to other people, they are not viewed as insular by people. It is not viewed as a lesser of two evils, it is the faith of many of the core, almost all of the western core as mentioned is Ezrite. Occult or hidden knowldege, perhaps the third sect but even this does not apply. The Church of Ezra is open in its teachings and open in its goal to spread the faith of ezra.