Hardware, performance and value wise Steam Deck rolls all over the Nintendo Switch (for base model). The NS hasn't got many price cuts and is rather old in terms of tech. Games prices too are in favor of the Deck as there are so many games on Steam and playable on the Deck. On average you can find games much cheaper. With an abundance of third party games a fraction of the price on NS and other consoles. However its not for everyone, the thing can be temperamental when it comes to software and certainly isn't a plug and play experience you get with something like the Switch.
It is a PC however, so there's so much more you can do with the device. And it being a open platform you can play and around and tinker all you like with it. Different devices though for different audiences.
For their respective audiences I don't think either overlap though. Like the people who are interested in the Steam Deck, are likely to be already Steam PC users who have some knowledge on PC gaming. And on the other side Nintendo gamers and the average joe who plays games know what to expect from a Nintendo console.
I do think it should be time Nintendo should release a new handheld with updated specs. With new games and engines on the horizon, Nintendo should be in there faster to get ports from third parties day one. Rather than wait and try catch up again with current gen consoles and PC.
