Look, I want a Steam Deck from the deepest depths of my heart and I love what it offering... but this take just isn't it. The Steam Deck is said to have sold "multiple millions" of units, lets say generously around 10 million. The Nintendo Switch has sold 132 million units. The Steam Deck couldn't hope to begin threatening the Nintendo Switch.
Though in all fairness, I don't think it needs to. It's much more of a specialized device rather than something you give to your kids.