You're comparing sales of a product in a nascent category (PC gaming handhelds) produced by a company with near zero retail presence with a marketing campaign almost entirely focused on their existing (Steam) user base to
Nintendo, a long standing retail giant that has dominated the market for decades who follow an entirely different business model. That's not to say they're
incomparable, particularly in how they provide value to consumers, but there's a whole lot of context that makes the business case more complicated.
Valve might not directly profit from the sale of GPD, Aya or Asus PC gaming handhelds, but they still get their percentage from every Steam software sale made on them, other stores notwithstanding but lets face it, they continue to dominate that space. It highlights that it's not specific hardware that Valve care about as much as broadening access to their storefront.
It's not the hardware itself you should be keeping an eye on, but rather how many platforms on which Steam is available.