I just don't agree that the RTS games made within the past several years have been underwhelming at all, especially when compared to other genres.
Hell, just look at MMOs, they haven't changed at all for the past 15 years. Literally almost no innovation whatsoever. Look at fighting games. Look at competitive first person shooters. As if those titles have been any better? I can't think of a single genre off the top of my head that, within the past 5 years, that has done anything amazing. The exception to this might be the roguelike genre, which has been producing game after game of innovative excellence (FTL, Darkest Dungeon, anything related to XCOM, etc.)
But the RTS games that have come out in that time have been solid, or have been re-released/remastered in such a way that its major flaws were addressed. Company of Heroes 2, PA: Titans, Grey Goo, Starcraft 2 (and expansions), Dawn of War 2, Wargame: Red Dragon, and now even Act of Aggression has been revamped to satisfy its audience.
Perhaps people's standards are too high? Really I think the greatest problem with the RTS genre nowadays is simply the lack of interest, not the quality of the games themselves.