If you employ a "preload then rehydrate" data sync paradigm then you should never see a blank page -- except on initial JS load. This is just an improper data sync strat and has nothing to do with SPA.
"Devs are doing SPAs wrong" is irrelevant when 90% of devs do SPAs that way. That it's wrong doesn't help the fact that most SPAs have garbage user experience.
I built a lib specifically designed for this strat: https://starfx.bower.sh/learn#data-strategy-preload-then-ref...