Was just checking "Where's this aircraft coming from" on the UA website.

My flight leaves in a little over 24 hours.
The plane (Boeing 777-200ER) currently just departed AMS for EWR, and is still yet to fly EWR-SFO, and then back SFO-EWR before we board.

Was wondering now how much time a UA plane is actually in the air as a percentage over the course of its usable life, incl. re-painting, maintenance, retrofitting, etc.?
And whether UA does better, the same, or worse than other major airlines?

(P.S.: excluding Covid parking-up I guess...)