I don't mean to be rude, but anecdotal evidence means very little. A hypothesis with anecdotal evidence alone is not testable.
We know scientifically what causes listening fatigue and the simple presence of a metal dome is not one of them.
Listening fatigue is caused by severe peaks in the treble or midrange. This can be caused by diffraction, breakup, acoustic interference, etc. Most speaker designers are more than capable of dealing with dome/cone breakup and the other issues can be dealt with via smart design. A 1" metal dome tweeter will not begin to breakup until far past 20khz because of its small size and adequate stiffness. Most people can't hear past ~15khz anyway (WELL before 99.999% of metal domes have issue).
While you might have a problem with these speakers, it is highly unlikely that the metal dome alone is responsible for this. There is no evidence I have ever seen to suggest metal domes are inherently plagued by response issues that cause fatigue. If anything, a properly designed metal dome tweeter will bring out more detail than its silk/soft dome counterpart as it remains pistonic through it's entire frequency range. Plus, not all metal is equal. Beryllium is a metal and a 1" beryllium dome doesn't breakup until ~40khz. Good luck hearing that!
Out of curiosity, what is your favorite speaker you have ever heard?