It will get more worse, with Proton there is no value in e.g. using Vulkan, just use DirectX, and the convinience of modern GPU programming tooling in Visual Studio, HLSL code completion with CoPilot, PIX debugger, and then let Valve have to worry about running it on Linux.
reply> with Proton there is no value in e.g. using Vulkan
replyValve themselves seems to disagree with you here, considering they still have Linux native SDKs available for integration, and are releasing their own games with native Linux support.
I'm guessing if what you say is true, Valve would be the first to move towards that reality you paint, but we haven't seen that yet, I'm doubting we'll ever see that, but the ones who live will see I suppose :)