What about Beryllium? What sacrifice is made with that material?
Beryllium was used in the Yamaha NS1000 - so proof that these designs can sound extremely good. The success of the Wilsons and JMLabs are also proof that they work extremely well (and B&W's diamond tweeter to add to the list) - I think they made the Yamaha's for 20 years or more. However, there is still a trade off - rigid piston (but downside is resonance) versus damped but flexible (downside is early breakup early beaming - limited bandwidth). At the high end BOTH can sound great. At the low end - a silk dome usually wins hand down. Some people can hear the difference on strings - some people can't - it is not always a fair comparison because even the frequency response behavior is different. It is a very complex subject because even ultra thin and light beryllium can have flexural problems depending on the voice coil to cone ratio - making it less than an ideal rigid piston....so shape is a big factor too.
Do WP, JMLabs with metal tweeters sound great - YOU BET THEY DO!
Can you hear imperfections in any speaker - yes - more or less there are no perfect ones....just trade offs.