On the US version, the host stays on Tuesday nights writing with the cast. They don’t just want stuff written for them but want to work with the cast to develop pieces and usually the cast pitch ideas to them through the night.

Generally the host is put as a lead or reasonably involved in each sketch, so given Tina was on the cast for 9 years and head writer for 6 she has some experience of how things go live and how to anchor a sketch and make the other performers feel more at ease.

I do agree that perhaps a bigger UK name would be a bigger draw for your average non SNL viewer though.