What is this speaker doing right?

Wharferdale uses really smooth and low compression tweeters and don't get  enough credit for it. 

Or, the Dentons are in fact better to your ears. Perhaps not set up optimally, but it doesn't surprise me that you are enjoying them so much. 

Welcome to variety in speakers. The LS50 is 79Hz +/-3dB. Bass MIA.  I would not tolerate that much of the music/bass lost in my home, unless there was a subwoofer with them. I do not care how pretty the rest of the spectrum is, if you drop fundamental low end you're not doing justice to the music. It's easy to sense that things are separated when there is little bass. 

The Denton is at 44Hz +/3dB. Welcome back bass! Imo, what you seem to be calling "phony mid-bass warmth" is actually a part of the music the LS50 drops entirely. I can see perfectly why the Denton is more enjoyable in some respects. I remember way back I had a Rogers small bookshelf, a very engaging small speaker. Though I have not heard it the Denton strikes me similarly. I reviewed some speakers in the Wharfedale Opus line, and they were also very engaging. 

Perhaps you mean "coherent" rather than euphonic describing the LS50, because your reaction to the Denton shows that it is tremendously euphonic to you. 

These are two very different flavors of experience in small packages. For the fun of it try the Wharfedale speakers upside down, and with tweeter to outside, then inside, to see what you think of that. Easy, free variety. 

Well it’s the next day and I’m still enjoying the Dentons more. 

You are right that the tweeter is smooth. The speaker is also less fussy with placement. It’s very musical. While the KEF is more analytical and accurate, the Dentons are more enjoyable to me. 

For claification, the euphonic description referred to my tube system driving PSB imagine t2s in a dedicated room—not the KEFs. 

The LS50s are a great speaker. But if I had to live with one I’d take the Dentons in my room with my setup.  

And for for the record I would recommend the KEFs to others.  I’d also say folks should be snatching up Dentons for second systems as they are a great value, well made and sound delicious.  

Look at all the nearly unanimous praise heaped on the LS50's.  It's the epitome of what I've come to call the "modern sound".  Some of us are coming to the conclusion that older models (or older designs) with a different design or design goals, sound better to our ears, whatever better means.

Twoleafers 

I think that t is well said. The KEFs sound pristine and modern. I can not fault them. They are great speakers. It is just that I’m enjoying the body and charm of the Dentons.