[Brightcolours]

1st off... the R5 is ready to make a photo within 1 second after it is switched on.

That might indeed not be fast enough. Especially if the EVF stays black during startup and you can't see where you're aiming.

Out of curiosity, I just checked with the D5: the delay between switching it on and the shutter clicking is basically zero. I assume it's not any different with a 1D-series camera.

Besides startup times, the biggest challenge for any manufacturer trying to bring a pro ML camera to market will be battery life. On events I took the D5 to (racing), I managed close to 5000 shots on a single battery. I don't see numbers close to that for any ML camera too soon.

I wrote "within 1 second" meaning less than a second. It is more or less instantly (about half a second it seems).
Any EVF will be black during before and during startup.... That is mirrorless for you. Nothing a Z9 can improve there...

Indeed, the increase in power consumption with mirrorless cameras due to EVF (so: imaging sensor constantly using power, EVF/LCD, all that data computing constantly) will always make mirrorless less efficient than OVF DSLRs.