This article includes sales estimates for different handhelds from market research firm IDC.
They place total handheld PC sales of the Steam Deck, RoG Ally, Lenovo Legion Go, and MSI Claw at almost 6 million units for the past 3 years. It’s estimated that the Steam Deck makes up between 3.7 to 4 million of those sales, more than all the other major handheld PC manufacturers combined.
There’s really nothing much better on the chip market if you’re concerned about power/battery life.
Valve has no reason to get into a hardware pissing contest. They just want to grow the Steam pie so don’t expect a SD2 until there’s a compelling difference.