Thankfully, the only company that I believe has ever made an attempt to make something load faster by making it functionally worse is Microsoft with Windows Fast-Startup.
"Ah yes, I know how to make their OS load faster... We'll just never shut it down!" - That's Microsoft-tier intelligence right there.
No, I do not believe that Valve would make their storefront worse in any sense just to beat Epic Games; they frankly couldn't give less of a shit, because they know that the EGL is not competition.