CS:GO is actually their biggest game now, but it does look like Dota 2 is dying. From a business perspective, they don't have any reason to try and save it though. They've lost ~40% of their players over the past 4 years, but are making more money than ever. The in-game tutorials have been unfinished for years, their Dota+ subscription service is all but abandoned (but still bringing in millions of dollars a year), and even cosmetics are mostly contained to a time-limited battlepass to take advantage of FOMO.