Anyone can get the performance crown by having an unlimited energy budget. Performance per watt is much more valuable in data centers (TCO) and consumer devices (battery life).
The Mac Pro does have a rack-mounted configuration for the non-desktop data centers case. (I have no idea whether people will actually use it that way, but it exists.)
I can see those being bought up for Datcenters and CI use. There have been companies hosting huge racks of Mac minis for ages to do CI for MacOS and iOS software.
Not always, if you are connected to a source of electricity and doing something limited by speed performance is critical.
For me, Desktop use is almost perfect on Apple due to battery life and perf but professional use is much better on Intel/AMD+NVidia. Also you could get much more perf for $ on such machines
Something with intention to make you money and directly related to powerful machine, i.e. writing code, editing videos, images, etc. As opposed to casual use where you plan simple games, browse internet, etc.
'plan simple games' so are you counting complex games as professional use in your example?
Let's say I'm a professional researcher for some oil company. My job will primarily consist of browsing the web and writing stuff up, does that make that job not fit into the 'professional' category? You're being paid to browse the web and just report on what you found....
I'm a professional that gets paid to do things and a MacBook Pro with M1 Max works perfectly for me. This whole 'professional' thing is absurd and full of holes.