- по Heroes 3

I think you're overestimating the strength of the Swamp as a town; its units are weak (except for the Mighty Gorgon).
In my opinion, the strongest towns are Tower and Inferno.

There are no strong or weak towns in the game – there are only weak and strong players!! I can easily (if I'm lucky, of course) defeat Necropolis, Inferno, and even Swamp with Swamp! So, I repeat – it all depends on the player's skill level!