FWIW,
I commented out the body transition (the fading text) and I think it looks OK (and maybe feels faster) when there is no body transition. Six one, 1/2 dozen of the other…
// body #main-outlet {
// transition: opacity 0.2s ease;
// }
// body.loading #main-outlet {
// opacity: 0.2;
// transition: opacity var(--loading-duration) ease;
// }