MK1 didn't have a story once and nobody flinched.
"How many army soldier women can MK successfully incorporate into its story?" is a valid question.
I think part of the answer to that question is the fact that we saw actual armies on the march in Outworld. The games might be moving away from a tournament format, and NRS might be allowing the world to breathe, realizing that the logical next step in the MK universe is for Earthrealm to organize a militarized defense in case some asshole like Shao Kahn tries to invade again. If this is true, and the scope of the games is getting bigger, then a more militarized roster makes lots of sense and there's plenty of room for both Sonya and Cassie.
So I'm not prepared to judge Sonya's involvement based simply on her past as a boring character. I think NRS are ambitious enough to do better. But I do understand some peoples' reluctance, for sure.