On small maps, the Fortress will completely dominate the orcs, and Chaos initially does a great job of mowing down the Horde's units. Plus, hit-and-run tactics haven't been canceled: the scouts disappear for 3 turns in invisibility, and you spend 3 turns in a row dodging fireballs from the Fortress, and you can't do anything about it. An Elf, even without Wings, can still give the orc a hard time. Hafiz, with his gremlins, will negate all the advantages of the war machines, which are important on rush maps.
I played on Heroes of Might and Magic V for 2 years, and when I won 10 games in a row with the orcs, I also thought they were overpowered. Further experience showed that this is not the case. And there is balance in the Tribes of the East (although it hasn't been polished to the end, but that's impossible, Heroes is not Starcraft), which makes me incredibly happy.