I’m struggling to understand where your coming from with this complaint because out of the 6 games that have come out since Sonic 06 Shadow was only in two of them and he was barely involved with the plot of either. Like, are you going off of the twitter takeovers? The comics? His one appearance in the Boom cartoon?
Basically yes, all the games or media Shadow have appareared since the "Color era" (when they changed the cast again) have made him very one-note (A Vegeta clone, even though Shadow had more to him than that ) and/or just there to be there. Sega could do interesting stuff with him, but maybe outside of the recent IDW comic (which I'm not very familiar of admittedly, so feel free to correct me there if I'm wrong)), I struggle to think what Shadow did that is noteworthy, and that's the kind of the problem with Shadow as of now, he is only know THE edgy Sonic character that "ruined" the franchise for many and/or doesn't fit with Sonic brighter tone, and it seem like it won't change anytime soon, from what I seen atleast.
That's a shame imo, because Shadow is a character that I feel has still potentials if given the right setting & writting team, but sadly, the only game that could have that, Sonic Force, just failed in pretty much every regard when it come execution. Heck, you don't even fight Shadow Clone, he is beaten in a
cutscene by the real one. They had a good excuse to make a cool battle with him & Sonic and they didn't even do that! If it wasn't for Chaos Zero being killed right off the start by Classic Sonic, I think peoples would complains more about how Shadow was another mislead by the marketing of Force trailers, but that's another can of worm on it's own.
Also, Boom Shadow, the Lyric version atleast, is a total joke that come & go as quickly as it arrive and make you wonder even why or how Shadow was put into this game in this state.