Comment by TeMPOraL

Fair enough. On a fast enough machine. This is off-topic, but while on my beefy dev desktop I get similar times to you, this was absolutely not the case on a much weaker laptop I used sometimes during travel - and the latter is more representative of how regular people experience things.

(Also, FWIW, loading delay of HTML pages on said beefy desktop, as tested right now, are consistently about 750-1500ms for me.)

More on-topic, these times apply only when the pages are hot in the browser cache. On my desktop, the first-time switch between "drafts", "sent" and "inbox" takes around 3 seconds each, and only then it is instantaneous. So regular users are likely to experience these long Ajax delays more often than not.