She writes at a high level, her production is elite, her technical prowess on the mic is impeccable, the only thing she can't do as well Kendrick/Nicki is switch in and out of multiple personalities and modulate her voice so that she sounds like an entirely different person. But other than that, I'm not seeing much of a difference in talent level between her and the best of the best Stateside.
As far as her immediate competitor in the UK, I give Dave an edge on bar work and writing (Dave writes as well as Lupe Fiasco) but his rapping isn't as versatile as Simz. Nor is his production.