Player rating for tournaments across all installments of Heroes.

No need to guess... just create a commission from the top 5 players and, based on votes supported by facts or logically sound arguments, decide on the minimum score for this map!
For example, we could try this on the 6th stage of Van Koningen's campaign!!!

We can try, but any tournament participant should have the right to challenge the commission's decision by providing a better walkthrough themselves, for example, within a certain period after the official results are announced. But, based on the experience of previous stages, such a commission will probably not be very necessary.

And regarding the fact that this will be yet another system... what's so bad about that... in the end... I, like many others, haven't voted yet...
I hope there won't be any disputes, but you can always reset the voting and hold a new one at the end of the tournament!!!

A simple vote is not suitable here. To objectively cast your vote, you need to constantly participate in tournaments or their organization, carefully study the behavior of various systems in various cases, etc., and not just have anyone who happens to be around cast a vote. It would be better to organize an expanded commission (about 15 people), have a discussion, and then vote. That way, it will make sense for those who want to form their own views on the system and present it to a fair assembly.

It was simply difficult to choose a rating without enough material.

Only estimated information about the range of the number of participants (and their average number) is needed. Well, maybe also about the range of results. And, as it seems to me, there is already enough of this information.

I think it makes sense to choose from rating calculation systems at the end of the year, after the Van Koningen and War of the Vikings tournaments are completed.

The rating is the law by which the winner in Van Koningen is determined. And the law does not have retroactive effect.