Whether Isobel Steele is a strong actor doesn't really matter to me. What does matter however is that Liv, a very recent character, gets story after story while legacy character Victoria Sugden languishes in the background. Same with Belle, she gets story after story after story. But at least she's more of a core character than Liv.
Liv's alcoholism story for instance could easily have been given to Victoria. After everything she's been through in her life it wouldn't have been at all unthinkable for her to turn to alcohol after she suffered yet another blow when Adam left the village. But no, let's give another story to Liv instead. I have no proof of course that her being related to a Dingle is the reason for that, but that's my belief.
And the Dingle's may not be as dominating as they have been, but they still get the major storylines on the show. If not all then at least the vast majority of the big stories on the show the last decade or so have involved a Dingle, usually Cain, Charity, Debbie or Aaron.