How well does he sell?
Jim Zub is Marvel's go-to guy to take over titles that they have to publish, but can’t afford to pay for a more famous writer. Or in this case, a co-writer, such as Christos Gage, Slott's most frequent collaborator.
Yes, he may be cheaper than other writers, but he is a good writer and writes good dialogues as well. And he was the first writer who bothered to give Riri Williams a true personality.
I believe he will do a good job. I at least, have enjoyed everything I've read written by him so far.