First of all thanks for this list, I didn't know about the KEEP functionality so read up on it a bit, I found the following interesting read: https://rwijk.blogspot.com/2012/09/keep-clause.html?m=1
I can't really play around with it at the moment as it seems Oracle only (I think) and I'm not using that at the moment. Might also explain preference for last/first value of your colleague cause it seems more general available.
Question from my side, why is DENSE_RANK used in this case? Seems to me like RANK or ROW_NUMBER could perform better, since there is less to keep track off? Of course ROW_NUMBER could give different results if there are duplicates in the ORDER BY column, but in that case the MAX is also sort of an arbitrary choice.
I think he was an alien