I’m not so sure.
Steam could continue to grow, although I do think Steam’s long term growth will involve real discoverability, actually making it so people enjoy using the platform and making it the destination for Discord-style chat, hanging out with friends, and so on while also insulating you from people who you’d rather not encounter - I linked to a good outline of what that means in here. Basically they really need to show you some games you don’t already know about (that you will love) and that way it’s more than just the Amazon equivalent where you go to order the game you already know about. That’s how the platform grows faster than gaming as a whole, by growing player engagement with gaming. Why play on consoles when Steam can show you this game you’d never heard of but you now love and only cost $10-20…
…plus (if they actually fixed things) a really smart social system grown around those games that actually turns Steam community into a community you’re not extremely afraid to even look at. Tumblr shows me all the Life is Strange fan art (via curated listing/reblogging, some moderation, and just a bit of luck in community attraction) without most of the questionable or objectionable stuff that I might bump into going onto the Steam community pages - clearly that’s something where Steam should be the best place to go for game-related stuff and yet the service both attracts the worst people and lacks the tools to effectively filter, moderate, and create positive community pockets inside the wider platform (that are insulated from bad actors and content the community collective doesn’t want to engage with).
But, and it’s a big but, even if they grow with this new policy (which will increase the hate speech on the store - that’s a stated aim of the policy, to increase the volume of “stuff you hate” on the store) and without actually fixing their community issues, then they build a breeding ground for scandals.
Valve isn’t a public company so the business journalists (ie not Fox News or anyone looking to just stir up trouble but people who supposedly only care about the money stuff) writing about what is going on with this store full of just the worst media can’t hurt stock value but it can make the company a pariah (as @Atlas notes above). Somewhere you do not include on your CV as part of your employment highlights. That’s a problem. They’re already restricted to only getting engineers who can work in a dysfunctional flat hierarchy (as we see from many who join and quickly depart), maybe deciding to change it up from working under a dysfunctional taller hierarchy. Plenty hate the various stack-rank style things going on (even if some enjoy the way it can boost remuneration, especially if you’re doing well in the office politics and so get lots of people voting up your share of the profits as bonus that quarter) so it’s already really whittling down the candidates. That “I’m not going to highlight this on my CV if I leave in 2 years” thing, or even listing some small side-work you did to totally mask your employment, really can remove a lot of top candidates that Valve would expect to be there and keeping things rolling.