You make excellent points. By all means, I think you should take your DB coaches advice into consideration, first and foremost. I think what most people are feeling is, that you are being taken advantage of. They are offering advice based on that, the basic cake eating roles that the WAS plays. But like you said, all situations and dynamics are different. Only you know what is going on in your situation. We just get a snapshot, and it's displayed to us through your descriptions. Perhaps we are not picking up on things that you are, simply because we don't get that info or see it in your perspective.
From what you are explaining, more and more, it sounds like perhaps (and I am guessing here), you have a sex starved marriage? I mean, it sounds like you are fulfilling the majority of your W's needs. It sounds like she is very responsive to you. With the exception of OM, you sound like you are getting along fairly well. Is it possible that OM is simply fulfilling her sexual needs, and not much else? Has you DB coach mentioned anything like that?