I think you're right, but probably looks cooler for the general public this way. The Steam Deck, as many advantages it certainly brings, doesn't look that attractive, for some reason. Most mobile thingies today are very slim, it could be that. Also, in my experience, the size is perfect for children. I've heard of a few that don't like it and would prefer it bulkier, but most are satisfied with the setup. Not sure about what you've seen.
However, if some of the problems you bring up could get fixed with a thicker unit, I'd certainly vouch for it. Ergonomy is not much an issue to me because that can get fixed with cases, and there are a lot of options for those. You can get elegant dockable cases that offer decent comfort but also allow you to remove the Joy-Cons whenever you want like Supcase's, or you can get cases that offer interchangeable grips, like Skull & Co's.
EDIT: Thanks, dude, I needed a Switch waifu.
My bet with The_Liquid_Laser: I think the Switch won't surpass the PS2 as the best selling system of all time. If it does, I'll play a game of a list that The_Liquid_Laser will provide, I will have to play it for 50 hours or complete it, whatever comes first.
