Steam Deck outperforms the Switch 2 thanks to its superior memory and higher CPU and GPU clock rates. An additional aspect where the Switch 2 falls short compared to the Steam Deck is in terms of customization. The Switch 2 operates as a closed platform, which necessitates jailbreaking it to enable any customization. Yet, even with that, your options remain restricted.
Conversely, the Steam Deck utilizes the SteamOS, a Linux-based OS. This allows you to switch to Desktop Mode for installing a variety of tools that the Switch 2 does not support. For example, you can effortlessly set up alternative game launchers and emulators. Additionally, you can stream multiple services and even convert it into a Windows handheld. None of this requires any modifications to the system.