Yes, a Steam Deck is a viable alternative to a budget gaming PC. But if you would want to buy a dock and peripherals and keep it docked most of the time I’d say go with the PC.
For me personally, the biggest plus of a Steam Deck was that I didn’t have to get peripherals (because my living situation is a bit complicated at the moment). And they’re dirt cheap, got a used LCD512 GB one for 320€.
edit: I own a laptop too. If I didn’t, I would’ve gotten a new one