Play against Necropolis.

Well, if you're going to counter something, then only use Darkness. Because summoning units on large maps doesn't make much sense when Cyclops can take on dozens of them, and a single Phoenix is more likely to be a joke. But things like Subjugation, Berserkers, and large numbers of units really come into their own.
Otherwise, everything is correct; a maximum-sized map is almost a guaranteed win. There's just one small "but." It's possible, though difficult, to arrive on the 4th week and rush with Orson; for an unprepared Orc, that's a death sentence. Just keep an eye on the tavern for a powerful Necromancer, and you won't have any problems.