It may not be my favorite game, but I think Starcraft 2 and its expansions deserve the crown.

Its been so well known, polished, and well-aged that even a decade later, I'm not sure there's much room left for others in the genre. This is Wikipedia's list of real-time strategy games by year. If I go through this list starting in 2010, there aren't many games here that I have even heard of. Here is the list of those I have.

2010: 5 SC2, Command and Conquer 4, a Sins of a Solar Empire expansion, Supreme Commander 2, a Dawn of War 2 expansion

2011: 2 Stronghold 3, another Dawn of War 2 expansion

2012: 2 Major expansion to Sins of a Solar empire

2013: 3 SC2 expansion, Planetary Annihilation, Company of Heroes 2

2014: 0 I haven't heard of any RTS game or expansion that released in this year, despite at least 5 being released

2015: 3 Grey Goo, Planetary Annihilation expansion, SC2 expansion

2016: 3 Battlefleet Gothic: Armada, Ashes of the Singularity, expansion to Ashes of the Singularity

2017: 3 Halo Wars 3, Dawn of War 3, Tooth and Tail

2018: 1 They are Billions

2019: 1 Anno 1800

I excluded things like mobile games, tactics/battlemode games, Anno 2070 and 2205 since they have almost no RTS elements, and 4x games. So there's obviously room in the gaming space for MOBAs, 4x games, and tactic games like the Total War series. But I feel like Starcraft 2 never left the stage. Any RTS game using the same formula that produced Starcraft 2 is going to have a hard time breaking into the mainstream.