I think the latter might make it harder to make a movie about something. Warcraft has a very rigid, very well defined, and very complex story which is in all honesty, not that great. Like its not bad, but I wouldn't rate it as one of my top stories in video game history.
Overwatch is much looser defined and there is a lot more room for new stories as a result. You could make up a story without having to worry about breaking canon.