Player rating for tournaments across all installments of Heroes.

I didn't understand the question.

Let me clarify. Which ranking system will be used to determine the final placement? It's quite possible that the winner will be the same for all rankings (or maybe not), but for such a large-scale tournament, it's important not only to have a first-place winner but also to recognize the other prize winners, the top ten, and so on. And here, we can't rely on invariance.

So, either suggest your own option or support one of the existing ones.

Okay, here's a specific proposal. Combine the rankings from IronAxe and VDV Forever in a 1:1 ratio.
50 ranking points are awarded based on the VDV Forever system.
50 ranking points are awarded based on the IronAxe system (days * 50).
This way, the requirements for differentiating participants with the same number of days and the additivity of the stage results will be met. Moreover, this system is easy to use and understand (ranking for placement + ranking for days). The addition for progress in a multi-stage tournament proposed by AlexeyPank is not acceptable.