I have both.
At the moment we have a couple of A9's, an A9II, 3 X A7III and an A7RIV.
The A7RIV produces unbelievable image quality but the A.F is a bit suspect, this is the second one I had had, the A.F is better (more reliable) on all of my other camera bodies and I include the A7III in that even though it doesn't have real time tracking.
The A7RIV kind of reminds me of way back when I had a D800, at the time I also loved the image quality but the A.F was always a bit hit or miss, but put up with it at the time as the image quality was so good compared to what else was available at the time. I feel exactly the same about the A7RIV.
I bought our first A7RIV for one particular job and sold it on again as found the A.F was too unreliable to use at weddings for me, the file sizes are also too big to be manageable. I ended up later on down the line buying another one as the same client came back to me for another similar job. This time after the job was completed I decided to just hold onto it but use it in a different way. It does come to weddings now but I only use it for the speeches, and for details, it also works as a back up. I find it useful for the speeches as the APSC crop mode gives extra reach which for me is useful as it means having to carry around less lenses. You can also crop for days and with the speeches in particular there is often a lot of distractions on the tables. The same thing applies for shooting details. It's an awesome camera for slow, careful work.
I rarely shoot studio stuff any more but occasionally we will do headshots for clients for Linkedin etc and the A7RIV is great for that too.
Just like the D800 I had back in the day the A7RIV feels slow and cumbersome to use, although to be fair I have become so used to using the A9 that anything else is probably going to seem slow.
I don't regret buying the A7RIV I needed it for the clients job anyway and the job cost covered the cost of the camera so I guess I could say I got the camera for free as I would have had to have bought something else similar regardless. The original A9 is still my favourite body and if I needed to buy another camera body would still be my number one choice. The A9II is just the same thing only more expensive, none of the small differences make any difference to me.
