Play against Necropolis.

It's so frustrating, the maps they play on are ridiculous, with random secondary skills and dwellings, especially...

And they really are ridiculous. You need to play on XL (hopefully you've read what's being discussed) without computers and without secondary skills, and most importantly, for several months. This kind of game certainly demonstrates the player's skill (you have to build a Castle, after all) and the diversity of factions, because battles of 10 units against 10 units are always so diverse. And of course, the years and tens of thousands of games played in Heroes 3 on random maps were a terrible waste of time. Long live a game with 3 native Castles, heroes of level 39, Psionic will teach us all.

especially...
it will be cool if the same Knight gets a native secondary skill...
it's interesting what the Necromancer will do in that case

Most likely, he will kill the Knight, and that's it. But the Demon will almost certainly kill the Knight.

it's especially interesting if this is at some kind of championship

So many championships have already been held on XL random maps, they have already gained so much experience... And on dueling fixed maps, all these discussions still don't make sense, they won't even get to the secondary skills.
If you play on regular templates, some Castles will dominate. If you play on the ones you suggest, then others will, and with even greater certainty and a more boring game. If you like it, go ahead.