They have some good quality of life suggestions in the video, but also a lot of horrible design decisions.

I do like the idea of displaying the review ratios on games instead of "Mostly positive" etc. and the expanding info when you hover which moves the add to cart button is a problem Valve could fix. But that's like the only takeaways, everything else was a downgrade, while I can see where they are coming from with their ideas... they are just not good UX. Their design is a case of wasting space and minimising the amount of stuff shown, they just outright remove useful information because 'it exists elsewhere'. Just because it exists elsewhere doesn't mean it can't be somewhere else to be seen at a glance.

They mostly looked at it from a design perspective and not a functionality perspective, they are new to Steam it seems from their profile shown in the video, so it makes sense they don't really know what people want/expect from the application.

I think you're making the classic mistake of "all users are like me". I personally liked pretty much all of her proposed changes and agree with her that Steam's current offering is a mess of disjointed design elements. I find the layout noisy, complicated, and hard to navigate, while her proposals all felt intuitive.