Okay, so for the first time, I'm going to be the devil's advocate. Thank God the devil in this situation is microsoft 🤣 🤣.  I have a GPD Win 4. Even the 6800u version. The following were improvements, be it on my device, when Xbox full screen experience was active:
Biggest improvement i saw was in heat!! Specifically the cpu, but really, the whole device. I can max my TDP (30w), turn cpu boost ON (i boost only 95% using quickCPU) and run borderlands 4 (NOTORIOUSLY  demanding game) and temps never go above 80c. Hit 90+ even just idling or playing in desktop.
Fps actually went up on borderlands 4. In 50s on. 40s off
And games launch quicker, even if I have to hold xbox button to select window. As well as, cloud gaming just works more often. Less hit and miss. I've only ever been on windows, mainly because of simplicity with my set up, so, I can't and won't bag on linux based systems, but in my experience, the full-screen experience basically delivered what it said it would.

When you use Game Pass ultimate it has a cloud boost

1080p full resolution need

Kinanimal 1080p full scene what the k

Every other systems living in the memory of Xbox 360 you can't tell me that xbox 360 Kinect games didn't have really good graphics for the one with the kitty cat you can see the fur and it look like the vapor from its nose was on the TV screen

I've been told them that Xbox 360 is better than Xbox One and Xbox series they really did streaming games on Xbox 360 they could have did it for Less Price too and that's what makes it better

Cell Brokers a joke with a lot of money

Game Pass Ultimate cam improved system response on Xbox NAT Xbox live Silver games for gold platinum hit diamond radio

Performance improved when pay for Xbox live Game Pass Ultimate

I have my OG ROG Ally setup to dual boot SteamOS and Windows 11. Works great! I boot to Windows for Game Pass and SteamOS for my Steam games. Definitely a difference in performance with SteamOS. Either way, both work great for me for the games I play. Heavier titles I use my PC or XSX.

Many Handhelds like the OG ALly or the new XBOX Base model only have 16gb ram and are pre set to use 4 of that as vram. Now with the FSE you could up this to 6 without fear of running to low on RAM. Would that not make a difference on heavier games?

Yeah, bur using Game Pass games with Steam OS sucks