Well, this is sort of true. Current COH2 is IMHO a zombie like game. It is half dead since relic itself has abandoned its developement and the game its nothing like what it was before. But its alive in its own way of being because it has a bigger and (hopefully) better playerbase, with a lot of streaming and forums activity to keep the game active and loved. I see CoH2 as another step leading to better RTS, not a definitive game though.
Perspective. COH2 is an almost 7 year old game on a niche genre which retains players like many other games would love to. It's probably in the same realm as WC3 (forget that Reforged exists) occupying a solid 4th place behind SC2, AoE2 and WC3.
SC is a monster on it's own. Let's leave that.
AoE2 HD/AoE2 DE/AoE2 really pulls the number. And while the DE version was not spectacular it was fairly fine enough to not be the disaster that was called Reforged.
WC3 RE was a great but wasted opportunity to bring people back into the game. It's hard to find numbers with Blizzard games but it would probably be higher than CoH2. More so in the top portion of the competitive side of the game, probably carried by the Chinese.
CoH2:
https://steamcharts.com/app/231430
You want real zombie//dead games from relative important IPs?
Dawn of War. Homeworld. Planetary Annihilation. Supreme Commander. Sins of Solar. World in Conflict. C&C Tiberium/RA/Generals. Grey goo (old Westwood). Cossacks. Halo Wars.
Steel Division/Men of War are a different genre of strategy games focused more on tactics and "realism" (RTT) but have a niche smaller playerbase.
Paradox games (EU, HoI, Stellaris) are in a group of "grand strategy" type of games followed closely by the Total War series of games.
PD: I forgot some RTS but it's a group focused mostly on single player, such as base defense in They are billions or the Anno series.