The phrase Son of man is actually ben Adam in Hebrew. This can be seen in passages that are quoted in the N/T which reveal to us how they are rendered into Greek. A good example is Psalm 8:4, which contains ben Adam, and is quoted in Hebrews 2:6.
But aside from this, and what I said previously, I do understand that from the context alone the passage you quoted and posted from Mark in my first response appears to be speaking of the creation either way. However, more importantly, think about the impact of what I previously said when it comes to other critical teachings. For example, if the statement can be understood to mean Adam instead of man or mankind it still doesn't really change the meaning of the statement, but what would it then say about the Shabbat being passed down to all mankind in light of other teachings and principles in the N/T?
For a couple of quick examples, if by one man, (Adam), sin entered into the world, and death by sin; and so death passed upon all men, (for that all have sinned, (Romans 5:12)), then would not the same be true of the Shabbat? Moreover if Levi paid tithes to Melki-Tzedek through Abraham, even though Levi was merely in the loins of Abraham when this occurred, (Hebrews 7:9-10), then what of the Shabbat which was made for Adam? Was it not therefore made for all mankind according to this type of argument and thinking directly from the scripture? Were we not all in the loins of Adam when the Shabbat was made for him in the beginning?
It is not that there is much difference in meaning whether it is Adam, or man, or mankind, but it is that this is a doubling down with a more solid evidence that what you said in the first post is true.