Such a treble boost can be a clever choice for their typical target group of old men
Fig.6 Estelon XB Diamond Mk.2, spatially averaged, 1/10-octave response (red), and of Wilson Alexx V (blue), in JCA's listening room.
Even the good and diplomatic JA mentions it in its conclusion:
The Estelon XB Diamond Mk II's measured performance is very good overall, though that excess of mid-treble energy may complicate setup and system optimization.—John Atkinson
It must be said though it can be equalised quite well as its (wide) directivity is quite smooth:
Source of all above measurements: https://www.stereophile.com/content/estelon-xb-diamond-mk2-loudspeaker-measurementsf
That peak around 4-5 kHz is similar to the voicing of Sony's flagship headphone, fun on some music, too much on others. Fortunately they aren't my only headphone. Of course you can EQ it and keep others positive aspects of the sonics.
Same with these speakers of course, I also noticed the off-axis stuff, it's pretty good. The cabinet is fairly inert and the CSD is pretty good also so I expect related aspects of the sonics are too. I'm not in the age demographic for that treble peak, or the income demographic for the RRP though.
