Player rating for tournaments across all installments of Heroes.

But, at the very least, the organizers will have to decide which system to use for Van Kanigem...

It's not that complicated... Just flip a coin and that's it...

...and justify your decision

A monument could be erected for such a feat... :)

You cannot compare the incomparable. A single rating for the VK tournament will be far-fetched in any case, unless, of course, its wording includes a phrase like: "This rating in no way reflects the player's strength in comparison with others. Rather, it is simply for demonstration purposes and shows how well the player navigates the entire diversity of the world of Might and Magic!" :) Well, or something along those lines...

You can only correctly compare players who participated in all VK tournaments. Otherwise, it's like choosing the best soccer player among hockey players... :)