Not really - that it does what it does in a way that still represents a challenge for human players is actually rather remarkable and the result of a huge and very expensive development process.
And terrain is always an issue for an AI that has to cope with so many variables.
I am not even sure that this example is all that unrealistic - history is full of battles where much bigger armies were defeated because they regarded their opponents with such contempt that they abandoned all the niceties of maneuver.
And all the AI really did was the equivalent of firing some arrows, noticing they were having little effect (each volley only killed a couple of men in each of my units) and then selecting all their infantry and clicking on my central unit to charge - the sort of thing I'd do all the time if I didn't have an easy auto-resolve option and had to fight such one-sided battles myself.
Bookmarks