We spend too much time talking about tweeters

I do it too. I'm guilty.

Just saying.  85% of the sound out of a speaker if not 95% is not in the tweeter, but the marketing people have us talking more about them than anything else.
I think I understand where Erik is coming from. In terms of how much energy a loudspeaker puts out, typically relatively little is actually delivered by the tweeter. In terms of wattage, a typical tweeter might see 5% to 15% of the wattage that the amplifier puts our, right in the ballpark of what Erik said.

But imo the tweeter’s contribution to sound quality is disproportionately large relative to its contribution sound quantity.

My understanding, based on the research of psychoacoustician David Griesinger, is that the ear gets most of its information from sounds in the 700 Hz to 7 kHz region.

The middle of that region is about 2.2kHz, and the ear’s sensitivity peaks in the 3-4 kHz ballpark. So imo a lot of important stuff happens in the range that tweeters usually cover. Also there is typically a crossover somewhere in this general ballpark, and getting that crossover right matters more than which tweeter is used.

Personally I’m MUCH more interested in how well the midwoofer and tweeter work TOGETHER than in the solo performance of either. In other words, the overall system design is what matters... but system design doesn’t make for enticing ad copy like tweeter exotica does.

Imo, ime, ymmv, etc.

Once you hear a good tweeter you'll talk about it also. The Magnepan ribbon comes to mind. 
I agree with everything Duke said. Kind of to add to my original thesis, how many times have discussions about entirely different speakers been focused on their tweeters? Is it Be? Diamond? Ceramic? AMT?

It’s as if the tweeter itself defined the quality of the entire speaker, and goodness knows the cost on the high end can be exorbitant for such little devices!

The tweeter gives everything its definition, presence, air and dimensionality. Texture, tone, instrument voicing and placement are all defined by the tweeter. Maggie’s ribbon and B&W’s Diamonds excel in these areas...the tone deaf or the high frequency challenged need not agree. Worst tweeter designs I’ve heard are ribbons...sand paper comes to mind!