What is this speaker doing right?

You may change your mind tomorrow!

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.