The second stage of the "Van Kanighem" tournament.

Regarding online play, you didn't fully understand. There are two or three maps that are very interesting to play. And you can play them 50 times and not get bored.
In a serious tournament, players are given maps they have never seen before.

I haven't been to any Heroes-specific tournaments in a long time, of course. But if in a Varick tournament, at a serious competition, players are offered unfamiliar maps, they might still play, but it would be a death sentence for the tournament and it would never be held again. There is a standard set of maps, usually 6-8 (for duels), and from those, usually 4 are chosen on which the games will be played. And I strongly doubt that unfamiliar maps would be given at Heroes tournaments.