You have a level of cynicism for the process which is crazy for someone who hasn't left training.
Groups (at least in 2024) don't fire/let someone unless there is a big problem. It could be personality, speed, quality or some combination there of. I don't think you have any clue how much time, effort and money goes into recruiting and on-boarding people. Recruiting alone is 4 figures between ads, dinners, and usually a partner taking a day off to shepherd the interviewee around ($2-3k value depending on the group). Onboarding for my group is tens of thousands of dollars in med staff application fees. Groups aren't throwing that time/effort/money away for no reason.
The situation you described is IMO a tragedy, albeit a very believable one. If the group did not make clear their expectations for the associate (which I would be surprised) and the associate did not actually seek out feedback on if he was doing enough (less so surprised) then it was a comedy of errors and a real shame. More likely, that associate was legit not good enough.
I'm just going to throw this out there. PP is not easy. Not every one is cut out for time/effort/volume involved. Some of that is quality based. Some is speed. Some people really really don't have the personality to operate in that environment. In my short career spanning 1 PE group and now 1 PP group, I've seen 1 person not extended partnership. He is legit the worst radiologist I have seen in my career. Like imagine the dregs of your residency program, and then imagine king of those turds.
Not throwing stones at you in particular cuz I don't know you, but anyone who was the bottom tier of their training program is probably a bad fit for PP. That's on both the trainee for shooting for a job they don't have the means of succeeding in, and on the group for being stuck recruiting said turd. My comments refer to the middle two standard deviations of rads; if you are semi normal, semi-smart, and work hard then achieving partnership is a very high likelihood.