Form factor very clearly isn't the only consideration though, and when combined with the other factors it becomes very useful. The comparison here is of two devices for playing video games, and form factor makes a difference there. Back in the early 2000s, people weren't really comparing the GBA to the PS2, the Xbox, the GameCube and the Dreamcast. These simply were different markets. Likewise, the Steam Deck and the Switch are more comparable than the Deck and the PS5 specifically because of form factor, even though as computing devices the Deck and the PS5 are more similar (both are running custom AMD Zen 2 CPUs with custom RDNA 2 GPUs, for example). The Steam Deck is, in practice, only slightly more "a PC" than the PS4 is.