Imo the Steam Deck is superior to most laptops for gaming, including higher-end laptops. Does it get better performance than your i9, RTX4090 Alienware M-whatever? Almost certainly not. However, it's significantly more portable, probably has a far better battery life, has a god-tier integrated controller + keybind system, suspend mode that doesn't cause games to crash, and an OS will all kinds of 3rd party goodies like RetroDeck. And it's not very expensive either (relatively speaking).

If all you're wanting is to play games on the go, then imo the Steam Deck absolutely destroys most laptops despite its lower power. If you're wanting to do more than that, like you'll mainly be playing games at a desk/TV or you'll be wanting to use it for other tasks like programming or creative stuff, then yeah, a laptop is almost certainly better for mobile computing. However, if you just want a handheld with optional docked capability, then the steam deck is way better than any laptop imo.