The TAD is theoretically a better design than the B & W line as it uses a coaxial speaker for the mid-high frequencies.
You can not say a coaxial design is inherently better. The problems are just different. Actually coaxial designs are hard to implement because of interference of tweeter reflections from the cone. That is why almost always there is almost always are smoother response a little off axis, than on axis. In addition these reflections do result in Doppler distortion of the tweeter output. Paul Klipsch proved that and wrote a paper on it years ago.
I do think though there are significant advantages to using coaxial drivers in center speakers.
As far as Yamaha speakers they have had a following in studios, especially as mix down speakers.
I think they are not the worst speakers, but they have a forward balance and would not be my choice.
I think all this comes down to which defects suit different genres of music.
The BBC greatly influenced the "British Sound" Their need was for monitoring chamber, orchestral and choral music. The really crucial band is 1K to 9K. Any elevation in this band, even a small one, is a big problem for this genre of music. This I still believe to be a big issue. I can not tolerate any elevation in this region. It ruins the violins, makes flutes shrill, puts the brass in your lap and ruins choral music. It also ruins a realistic perspective. Whereas as slight drop in this region is not unpleasant at all, and avoids a forward balance. So the BBC avoided this problem like the plague and pretty much made certain there was if anything a slight drop in response at 3 KHz. This became known as the "BBC Smiley."
Now the popular music aficionados did not like this response at all and wanted a more forward balance and were more tolerant of an elevated response in this region.
This gave rise to the notion that different speakers were better for different types of program. Far Eastern speakers have on the whole had elevations in this region.
Unfortunately getting a really flat response in this key mid and upper band is one of, no I wold say the toughest challenges, in any speaker design and few speakers really achieve what is required.
I will say though that a speaker with a very flat response in this region, on and off axis will please both camps.
I note the engineers from the world of music I do not listen to out of choice are very happy checking and remixing from my speakers.
So basically if you have a deep, tight and uncolored bass, and a good power band response to at least 2.5 K and a really flat midband response then that is most of the loaf. Then a good phase and transient response guilds the lily. The trouble is that it is such a juggling trick of interdependent variables. Above a below that and I mentioned people seem more tolerant of slight irregularities. I emphasize slight.
I think Asian designers seem much more tolerant of elevations in the midband and upper end responses than the rest of us for some reason. Having said that though, Japan was always a big market for UK speakers. The bulk of the output of the JW drivers and complete speakers went to Asia, above even the home market. So may be the Asians do not have such love for that type of sound as one might expect.