Halo Wars 2, as a Microsoft first-party exclusive, sports a level of polish, gameplay diversity, and visual quality that RTS fans haven't been able to experience in a long time. This is a niche that Microsoft can capitalize on with a Halo Wars 2 release on a well-liked, highly-respected service like Steam. The opposite is true plenty of RTS fans exist, and many of them are looking for high-quality games to play that aren't Starcraft II. However, just because RTS games aren't as popular as they used to be doesn't mean that an audience doesn't still exist for them.
RTS games have been declining in overall popularity on PC ever since shooters rose to their dominating position in the multiplayer market.
