I've seen these mockups for a steam controller that is essentially a steam deck without a screen multiple times now and it looks like absolute dogshit. This would be far from "the perfect controller".
Yeah, I don't know why they'd use that image. It's so lazy and uncreative. That's not what it'll look like. They literally just cut the edges of the Deck and shoved them together. I've seen better concepts of how it'll look.
As an owner of a Steam Controller, it's actually pretty nice. It's probably the most ergonomic controller out there, though for functionality it hits a different niche than the typical controllers you find everywhere. Its better for some games, particularly ones designed for mouse, but worse for others. I'd bet on the Steam Controller 2 being very ergonomic and adding sticks, as well as the track pads, to be quite possibly the best controller available for every game (excluding keyboard and mouse obviously).
Like you said, these are Steam Deck prototypes, not the controller. They made a cheap controller with the same potential profile of the Deck without the screen because it's cheaper. It was to iterate on the Deck quickly and cheaply. They'd never release a controller like that. They do the same thing for all their products.
I would bet on the same hand grip bits and a similar set of back buttons. The touch pads will be revamped and it'll probably force the shape to change a lot.
I think the controllers sold relatively well though. Just not Steam Deck well. I know a good number of people who own at least one.
I mean, why not bring back the OG Steam Controller aswell? I still use it and it works great, and it is almost creepy how it handles almost the same as the SD.
Controllers always look like shit IMO. The PlayStation and Xbox controllers are weird bulbous slabs with buttons, but extended use has made them look normal.
I think most mockups make the mistake of keeping the rectangular shape of the deck surface, but add a few bulbous growths for style in areas your fingers aren't reaching anyway, and they all look like your regular old console controller
I've used my Steam Deck as a controller (via remote play) while sitting at my desktop PC. It is by far my favorite of the various controllers I've used.