I saw the slide this morning about how 2017 Wikitext editor performs much better as far as load time goes, compared to 2010 Wikitext editor. Most people on wiki however have this "impression" of how 2017 wikitext editor and VE are slow in general. I have a guess that that impression comes from seeing the loading bar. The standard editor could be a lot slower but since it never tells the user explicitly that it's taking time to load, people don't think it's slow.
I know that the loading bar is important when it helps to see if the editor is stuck (common occurrence on office wiki) so I'm not how this should work.
Take this ticket as a suggestion. :)