What I like in an other DAW is the really lightning fast startup when starting a new project. Its about 3 seconds.
In Ardour I have to:
This is okay, but IMO it could be optimized somehow. Is there a way to set a default startup session and audio settings? I need to be fast, when the muse hits me. 
Ardour5 --new /path/to/my_new_session
That skips the “recent” dialog.
The longest delay is usually the initial time spent to scan sessions for recent list (if some of those session files are huge e.g. > 100MB).
Preferences > General > Engine > Try to auto-launch audio/midi engine
That will use the most recent settings when loading a session. However for new sessions Ardour will always ask what sample-rate to use. But just pressing < enter > here to accept the most recent setting is quick.
One way out is to use JACK. If jackd is running and you’ve used jack in the past, Ardour will use it unconditionally.
2 sec is realistic, but 5? for a new empty session? What CPU and disk does that system have? Perhaps Preferences > Plugins > VST > Scan for [new] VST Plugins on Application Start
is enabled? That may add a few seconds if you have many VSTs.