Here are my thoughts on this.
1. This feature should have come in early 2020 - as soon as the pandemic hit - or much much earlier. There is absolutely no reason to have an additional external camera when the iPhone already boasts one of the best cameras that can be used for video conferencing.
2. This solution was not created for the iPhone to be mounted onto the MacBook. Older MacBooks (all kinds) have crappy cameras - that's true. Newer MacBooks (starting with 2021 14" and 16" MacBook Pros) have much better cameras. Mounting the iPhone onto a MacBook's thin screen makes no sense; it's a precarious position for an iPhone to be in: it could fall down onto the MacBook's Touch Bar or keyboard and either get damaged itself or damage the MacBook. What does make sense is either mounting the iPhone onto an external monitor or onto a stand.
3. Apple should not have put a camera or microphones into the Studio Display. That camera is absolutely horrible; the microphones (while not horrible) are significantly inferior to microphone arrays in the last year's MacBook Pros (and I would bet even compared to the 2020 M1 MacBook Air and MacBook Pro). Instead, Apple should have created a mounting solution on top of the Studio Display (maybe a pop-up mount with a MagSafe charging adapter) onto which an iPhone could be mounted and charged while being mounted. That would have been an elegant solution. Because Apple put a useless camera and sub-par microphones into the Studio Display, it had to put an Apple silicon chip in the Studio Display to control the advanced features in the camera and microphones. It would have been much better not to have Apple silicon in the Studio Display and instead have a charging MagSafe mount. The camera and microphones could be supplied by the docked iPhone and controlled by the attached Mac with the help of the Apple Silicon chip in the iPhone. Thus, Apple could have reduced the price of the Studio Display to a reasonable amount: maybe $1299. It really should cost $999 (pre-inflation), but with the inflation, $1299 is probably justified.
I have a 2021 14" MacBook Pro and a Studio Display. I use the microphones in the MacBook Pro (which sits to the right of the display, so the location of the microphone array is not optimal, yet it sounds much better than the microphones built into the Studio Display). I use the Studio Display's camera and speakers. The speakers are better than the speakers in the 2021 14" MacBook Pro but only marginally better. The camera in the Studio Display is inferior to the camera in the 2021 14" MacBook Pro, but because my MacBook Pro sits to the side (on a stand - used as another monitor), I am using the Studio Display's camera for work. However, when it gets dark, the quality of that camera is simply atrocious. It makes no sense for me to have paid for the camera in the Studio Display just to cover it with an ugly iPhone mount. That's just a terrible design of the entire ecosystem.
My preference would be to have an Apple 5K Display (call it Office Display - if you wish) that has no built-in camera, no built-in microphones, no Apple Silicon chip, but has a built in MagSafe charging iPhone mount capable of retracting into the body of the display. I would mount my iPhone onto that mount during my work day and take it off the mount when I am done for the day or when I leave for lunch. In this setup, I could use the MacBook connected to the Display in a clamshell mode - if I so wish - because I can leverage the iPhone's camera and microphones. When I work outside my office, I would just utilize the camera, microphones, and speakers built into my MacBook Pro and not bother with mounting the iPhone onto the MacBook Pro's screen. Or, I would use a tripod stand to mount the iPhone onto if I wanted to use a better camera while being outside my office.