Thank you for the numbers -> I agree these are slow, and I can guarantee you that the Jira team is working on it (though I can't talk about details). These numbers are definitely outside of the goals.
I appreciate the call out of "page to complete rendering and the progress bar at the top of the screen to disappear" and "until the issue, comment and buttons have all loaded". In a dream world of course, everything would load in < 1s (everything drawn, everything interactive), but working our way down to that will take time.
We're currently looking at each use case to understand the '(a) paint faster vs (b) interactive faster' tradeoff and trying to decide which cases the user has a better experience with (a) or (b). In Confluence this is clearer in some places than in others, but in Jira it's less clear I think (I work on Confluence, I probably shouldn't speak for Jira specifics).
It always comes down to a limitation of resources though, which is why we're always hoping to get as specific feedback as possible.