However, if I really want into macro - such as in Lembeh - I will use my 60mm.
Absolutely !! And I must add also the 45 mm Panasonic , which is a great lense too . With the Subsee +10 you can do really good macro even try supermacro .
As well that you can do very beautiful wide angle with the 8mm fisheye of Panasonic that I own or other dedicateced wide angle that I don't own , and that I've never try , so I can't speak about .
In both situations wide angle and macro you can't get the same result with the 12-50 , you can make excellent pictures with it , but not the level you can have with the fixed focal lenses .
Also versatility underwater is difficult , because jumping from wide angle to macro needs a complete change of mind , and adjustements for the camera and the flashes as well , it's extremely difficult and tiring . Better to go for macro OR wide angle before the dive.
I own also the 12-50 with the very expensive but so well built port and zoom gear from Nauticam ,I use it from time to time , but there always someyhing missing me especially in wide angle .
The OMD is really a great camera , full of possibilities , but you could miss something if you try to manage everything with the 12-50 even if it's a great lense , no needing anymore fixed macro or wide angle lense .
The OMD is not a compact camera , it's an interchangeable compact camera , so use it
Ps I hope that my english will not create misunderstanding ...