The A7C was the camera that got me into photography, I finally felt like there was a full frame camera that was small enough I wouldn't mind carrying it with me. Loved using it, but after a year I really started to miss having more hands on control, namely at least one more dial and button. Bought the A7IV and have been loving it for that, though I do notice the size a bit more (I know Sony's are relatively small compared to other brands).
The one thing I really missed from the A7C was the looks, since I had the one with the silver top. I liked that retro vibe sort of vibe, and the fact it didn't look like all the other A bodies just cut down features. Now that the new A7C has more hands on controls (we think) and I'd lose no functionality I need from the A7IV, I'm tempted to go back.