Power-wise Steam Deck isn't on par with current gen consoles nor even last gen consoles. It can play plenty of games, but we've reached a point that it can't run most new AAA games at an acceptable level of performance regardless of settings. With a console you can buy pretty much any game and assume that it will run at a playable frame rate (though there are of course exceptions).
Doesn't "last gen consoles" include the original Nintendo Switch? That thing was underpowered when it came out, let alone compared to a Steam Deck. Also, PS4/5 and friends are not handhelds.
And it doesn't have to be on-par. Show me a gameplay enhancement that the current gen hardware has enabled - something that just wasn't possible on previous gen hardware.