Yes, because the Steam Deck has the DX12 Ultimate featureset just like the next gen consoles, the 5700XT not. It's really simple and Mesh Shaders+Sampler Feedback are a huge, huge deal. Get a 8800GT and try to run a modern game on it. It won't run because the 8800GT only supports up to DX10 featureset level, and not DX11 nor DX12. The same fate is destined for the 5700XT at some point in time. Sooner or later it will happen.
Until then, we already have games that simply cannot run on the 5700XT because it lacks HW-Raytracing, like Quake 2 RTX, Minecraft RTX, Metro Exodus Enhanced Edition. All of these games are huge, huge upgrades over their original versions and you miss out if you can't play these and have to stick with the original versions. These games can probably be played on a Steam Deck (although at crazy low resolutions, but it would work)
And your post is also incorrect. We already have a confirmed title that releases without a rasterization path for their lighting solution as early as 2022.
https://screenrant.com/avatar-frontiers-pandora-ray-tracing-every-version/ Software-RT for cards like the 5700XT, better quality and performance with HW-acceleration for RDNA2. Steam Deck will benefit from this, a 5700XT won't. Many developers will follow that strategy because it saves a ton of development time.
Sorry, but your 5700XT is already dead. Steam Deck has all of these cutting edge DX12U features. Inform yourself about mesh shaders and Sampler Feedback and you will get why. Raw performance is not everything, especially with this generation.
Xe GPus do have Sampler Feedback actually. Intel held a pretty interesting GDC conference yesterday.
With Sampler Feedback Streaming they managed to stream 350 GB worth of assets with a ridiculous small VRAM footprint of just 230 MB. The future is now. The texture space shading part of Sampler Feedback also improves performance nicely and a 3D Mark featureset will soon be available.