That's basically how it was; you upgrade the snipers and go to the barricades. You say you buy 8 heroes, but it's hard to see how they broke through the dwarves and spearmen, and then captured the Castle...

Snipers can break through anyone; it's just that at the end of the turn, the hero who has already moved gives his troops to a fresh hero, who runs in another direction, clears everything, and passes it on to the next... not that he passes it on himself, but special runners are hired – those who have the maximum movement points at the start (Pasis, Pyre, Dessa, Gunnar, Kirre)... Ciele with the mana-boosting hat can even go with just one sniper; she has magic like a cannon, she doesn't need troops... but you need to spend the night with the fastest troops so that the next day you have the maximum movement points... and a bunch of other things... :) this is purely a technical game, focused on efficient gameplay – squeezing the maximum out of the available situation...

Yes, I received a huge slap in the face with these results...
Apparently, for me, this is just a game, and I still don't know much about the heroes...

Well, you shouldn't take the situation so seriously... ;) you were just playing on unfamiliar territory and, frankly, according to unfamiliar rules... after all, the technique for speedrunning must be developed through practice... if you play a little, read detailed descriptions from players who will post them here later, everything will fall into place...

Maybe my result is even laughable...

well, so far, no one has burst from laughter, as you can see... join in! :)