Stormbanner I expect to go. I'd get rid of it if I was doing the book. Skaven don't need it and it just about kills missile weapon units which already struggle in 8th edition.
Don't need it? It's very helpful, if they start they can just activate it later and use their own shooting in first turn. If they go second, then enemy artillery is neutralised. Even if it expires on next turn, then You're very close to get Your precious skaven targets into safe close combat.
Also, I believe that strength in numbers rule wasn't written with having in mind 8ed and steadfast, skaven were supposed to be cowards... I wonder what makes people think that they were almost 8ed book - only big must have models and release date, but in terms of rules?