This question was put on hold because it's specific to one website. I don't think the question is specific to just ONE site, but it applies to ALL sites that display a loading screen with height: 100%;
which covers all content and afterwards is hidden from JavaScript.
I deleted a short paragraph within the question that referred to my specific website, but kept the code snippets as they help clarify what I'm asking.
Moreover, there are other SO users that find my question worth answering.
LATER EDIT: I deleted the link to my website, and I see NO OTHER QUESTIONS ON SO REFERRING TO LOADING SCREENS.