Except that the "Watch All" menu item doesn't move to be the first item in the list for me, except perhaps when I have imported a brand new Series (or Season), and possibly a few other odd occasions. Very rarely.
However, if I select "Watch All", then the next time I go back into the file level of a Series, "Watch All" will be the first item in the list. Then if I select "Watch", the next time I go to the file level, again "Watch" is the first item on the menu. MC remembers the selection you made in the past, and offers that selection again the next time. That is pretty neat.
My vote is for "Watch All" to stay where it is, doing what it is. I don't use it often, but I do often drill down to the file level to read the description of the Pilot of a new series, and then if I have multiple episodes already, I might select "Watch All". I have never used the "Play All" menu item for Episodes of a Series. For a start, it requires and Up Arrow from the highlighted episode name, and a Right Arrow to get to it. "Watch" and "Watch All" don't require this extra navigation.
This discussion has happened before. Leave it alone thanks.