Hero leveling during the first 2 weeks.

Can you give a specific example?

Well, it depends on how the map is laid out; sometimes, if magic skills are good and there are mines, you can manage without reinforcements or artillery.
Here's an example Replays of battles for mages, including ones against ten angels (if I remember correctly).
Of course, with reinforcements and artillery, it will be easier, but it also depends on the map – naturally, I’m not sure everything is that easy in random maps, especially at the difficulty level of the current tournament, but maybe someone more experienced can confirm this tactic.
P.S. This is based on any standard maps and relatively small layouts, at Veteran difficulty.