Player rating for tournaments across all installments of Heroes.

Compared: one to one!

That is, 50/50. But Iron wrote that "equally" doesn't work... - see his post a little higher. Who should we "believe"? :)

Added 5 minutes later

Since the tournament is considered official if at least 20 participants apply to participate in it,

That's not quite right: the quorum has already been calculated - that's true, but there are fewer participants than previously stated;
for a Heroes III tournament, you only need 10 people :) and it will already be official.

In general, maybe we should calculate the rating depending on the tournament, i.e., directly from the task itself (speed, experience, skeletons)? Maybe it would be more efficient to calculate separately for each tournament; in my humble opinion, it would be easier to calculate "such things" in total.