Although the standard/expectation of celebrity dancing has jumped since the program began, it really doesn't improve the audience experience of the show.
I think the audience want to get behind an average, or below average dancer (Jeremy Vine, or Dan Walker ) and see them make gradual improvements each week and blossom into a reasonably good performer.
The celebrities that come on the show that can already dance are not giving an interesting 'journey' so are a bit dull to watch or get behind. Ellie won last year, because she was relatable, wasn't a natural to start with, and gave the audience a good story to watch.
With that in mind why put in someone like Layton, or raise the bar to generate impossible standards when this probably isn't why the audience is watching in the first place.
Watching the dancers on iPlayer with my dd on Sunday, we fast forwarded all the chat and fillers, watched who we liked and fast forwarded others. I don't think I watch Layton at all as we just were not invested in him, but we did watch Zara as my DD loved her story (she did look like a beautiful Disney princess too which did appealed to my DD) and she is more inspirational as someone completely out of their comfort zone trying new things.
And nor did we watch the show as a whole because the presenting is so very very poor, over hyped and too many fillers. We don't watch 'It Takes Two' as the formate and presenting are very poor too. I don't know anyone irl who watches strictly now, which is sad as it was once a really lovely show, but they have really lost focus on why people tune in.