[toni-a]

My worry is that you are exploiting only a tiny bit of Z9 potential with lenses used through adapter, you will see yourself moving to native mount soon

Why is that? The AF is very fast and seemingly precise. Of course the proof will be in the action, but hopefully I'll have the opportunity for testing soon.

And no, I don't intend to switch all my lenses to the native mount - I intend to keep the 1D as well. Besides, it would take another huge investment of money I simply don't have now, and hardly will in the next couple of years. Some of my Canon gear is unsellable anyway because it's so worn and old (at least three of the lenses, anyway - the 14, the 70-200, the 100-400).

My experience adapting Canon lenses to Sony wasn't encouraging, every lens behaved differently :
10-18 no functionning at all, 17-55 focus errors, 50f1.4 focus  hunting,  85f1.8 good but slow, 28f2.8 good but still slow, that's why I dropped the idea completely. OTOH Canon EF lenses adapted to EOS RP work perfectly, well just like they used to do on EF Canon SLRs 
When you get a beast like Z9 with world class autofocus abilities you won't be exploiting the camera full potential when it comes to autofocus speed with adapted lenses, unless the adapter is really really good or adapter/camera body firmware allow them to work together in a very good way.