In the end, Shepard is no different from all the other space marines that we've all grown accustomed to. Get the guns, fight the aliens, save the world. All the reasons you can give in making Shepard more of a character can be applied to any of the characters in the series. You don't need Shepard to tell a good Mass Effect story.
We're talking about Mass Effect
. The main character of Mass Effect
is called Commander Shepard. If there's a Mass Effect
movie, it's going to be about Commander Shepard, not about Random Salarian #342. It's not a value judgement, it's what is likely to happen.
Sure, I guess you could tell any kind of stories in the Mass Effect
universe, and yes, I guess you could also make a Harry Potter
movie about a family of magical dancing frogs, but the only point of doing a movie adaptation of Mass Effect
is to bring to the silver screen a close approximation of some of the elements that people enjoyed about the game. Featuring the main character is one of those elements. It may not be what you'd like to see, but it is at least somewhat rooted in reality.