As for skill to ego ratios, when I was instructing hapkido and kumdo at a Korean school, myself and every other sadan and higher instructor that were there were introduced by the GM as "Master."
...which is not the same as introducing oneself that way. I rarely introduce myself as "Doctor" but am often introduced that way by others. (Physicians are a special case w.r.t. that title as it also signifies their application--indeed, in many Commonwealth countries physicians have baccalaureate degrees but are accorded the title 'Doctor'.) I'm not trying to prohibit anyone from calling themselves what they want. I'm saying that in my experience those who introduce themselves as 'Master' are generally letting me know that they're not strong enough to let their skill speak for themselves. Again, there have been exceptions.
If for a WMA it's the right title, then by all means use it. My experience in this is limited but fencers I have met have been more likely to be addressed as "Maestro"--clearly a nod to the culture of origin--or to say that they're a master-level instructor, not that it's important that I so address them.