Brook should win it with relative ease, but Jessie has improved immensely since his loss to Bradley, so this new Vargas I'd give a small chance of the upset.
I think this is a good fight for Brook, I don't think much of Vargas but he's a name fighter (due to his hail mary last round vs. Timmy), a decent scalp for Brook
At least it's a step up in competition for Kell. But I could name at least 5 worthier opponents at WW that I'd like to see Brook in there with. Still, it's the best competition he'll have faced since the Porter fight.