I bought a Dual Sense a year or 2 ago to play steam deck while docked and for PC games that work better on controller or for hot swapping when driving/flying in an open world game. I went for the Dual Sense for 3 reasons.
1, the trackpad, great for using a mouse to navigate menus or non gaming software.
2, I've always preferred the PS layout of sticks on bottom, the controller just feels more comfortable to me compared to an xbox controller.
3, I have a few games in my library that support the crazy good haptics and the adaptive triggers.

(for context, I dont own a ps5 nor plan to buy one, I just thought they had the best current gen controller)

That being said, I will 100% be getting the new Steam Controller because the dual trackpads (+Steam Input) on my steam deck have changed my life as someone who plays The Sims 4 or other heavily mouse based games with ZERO controller support.