That's not really apples to apples since one will be locked to the manufactures store and have all the sony games day 1.
I love my steam deck which is probably why i won't get the playstation handheld, i'll just get the next steam deck.
But I bet Sony may see this as crossing the line. Steam is coming into the living room, with more games, some sony games, all xbox games, and probably not charging for online multiplayer . . . that's a threat that could make playstation change their multiplat stance some. GaaS would still probably go everywhere, and things like MLB and Lego Horizon. So still multiplat some.