I was pushed into 12.4 and I regret it. What's the improvement? I don't know - I haven't found it yet.
What are the drawbacks? One can no longer set "Neutral" (or any profile aside from Color or Monochrome) as the default starting point. I guess they decided we want the Adobe engineers to initiate the editing process. One reason I shoot RAW is to have control over the image.
It appears they have completely illiminnated the perspective control tool. Can this really be true? Am I just missing it somewhere? If they did indeed delete it ... what in the world are they thinking?
This is a user to user support forum so you're not being too effective addessing your 'concens' here, there is nothing we can do but help you revert to the last version you refereed. You should go here: https://www.adobe.com/products/wishform.html
As for how to setup camera profiles as defaults, try this video: