I am surprised by the statement for sure. The PC-like environment of Deck allows for incremental upgrades like any other PC. They can do so much more with the handheld format. Maybe this does not rule out a minor revision but still disappointing. IMO they could definitely experiment more with the form factor. The hard work is done. They've managed to create a PC OS fitting for a handheld fairly well. I can't imagine what the smaller Chinese manufacturers are doing to be particularly resource straining.
If you want high-end handheld gaming, Deck will be a hard recommend the coming year considering what's out there now.
A handheld is not a modular device and there are downsides to just chucking HW out there (which you are seeing from multiple vendors not the same one) which has a cost in and of itself.
Valve is avoiding the waste of iterating on the HW, deliberately choosing a console like HW generational approach but allowing deep software customisability at almost all levels (best of both worlds), and investing resources in the OS, in the UI, in the features such as game controller layouts, in the drivers (they had fixes for StarField right away while some other Windows based machines also using a similar chipset did not). You are severely underselling what they are doing.
I think by the time the other handhelds get serious usage by devs you will see a Steam Deck 2 with much better specs and yet a great cohesive and polished experience and integration. They actively work to make sure you know how the game experience is on Deck and trying to improve with with and for devs.
Valve made a very well rounded and thought out machine, but yes not going for the highest possible spec at every second.