Even without any search, you can come up with a lot of problems: Will you calculate an alternative route as soon as a route gets blocked? What if it is a friendly unit? Should it move to open way? What if it's already moving? What if it's too slow? What if there are more, moving to different locations with different speeds and priorities (For example: A tank going to help defend the base vs. a resource gathering vehicle)? What if the blocking unit is an enemy unit? Attack it or move around? Can I attack while moving? What if I can't move around? Can I crush it? Am I part of a formation? How to pass through a narrow path? Should formation alter?
As someone who has worked on an RTS, among other games, I think I am qualified to speak on the manner.
For starters, yes there are complex problems with lots of edge cases indeed. But not one of the many problems you suggest are computationally difficult. Now there are some computationally difficult problems to deal with in an RTS but those are not among them.
Additionally, a large amount of the problems you just listed are common among any game with AI. RTS pathfinding is hard, but so is pathfinding an an FPS, and then add in how much more complicated a level is in a game such as Assassin's Creed, to the more simplified structures you can manage in an RTS, and it's easy to see why this isn't simply a matter of RTS games being simply more difficult.
And within an RTS there very many problems that are much easier, both from a complexity, and computationally then in other games. Visibility determination is one thing in particular that's considered super difficult, and very performance sensitive, that's very easy to solve with the fixed perspective of an RTS.
And then there is networking, in which case you can use a lock-step model in RTS due to being less sensitive to latency, that both vastly simplifies networking. And also makes it possible to synchronize the large amount of units in an RTS with minimal bandwidth.
I think I understand. I still play AoEII only so I wouldn't know Assassin's Creed. My idea is that it would be complicated if you have massive amount of units. The calculation could be very expensive when most units are moving. As I said, that's just my idea because I'm not a game developer.
