merge layers

Similar/related operations being spread out over huge distances in the menu would seem to be a user experience issue of its own. 

And as @D Fosse recommended one should use shortcuts for frequent tasks anyway. 

While one can not reorder menu items under 

Edit > Menus

one can hide them altogether – if they become needed cmd-clicking the menu should reveal them or one can use »Show All Menu Items«. 

Make custom shortcuts to avoid the whole problem.

Two-key shortcuts like command-e (merge) can be done with two fingers; at least merge visible requires a little more coordination and intentionality when pressing three keys -- shift-command-e.

Flatten image has no shortcut.

Merge layers is grayed out if one of the layers is unselected.

To further complicate, merge down rears its head if more than two layers exist and only one is selected, making where you are in the stack important.

Stating the obvious because it's not and fraught with danger!

To me it makes sense to have the commands near each other since they are similar in nature. Personally when I need to quickly merge I use the keyboard shortcut cmd+e (mac). If it were to be moved, where would you propose it go?