I'd still recommend to get Roshi.

He's useful in any kind of battle, pvp, Ranked, SWB, GNW.

He doesn't shine too well in arena, unless you have a good team for him.

His kit makes him a long run, worthy ninja to be recruited.

Kage - they still give you good buffs in general. They work well in arena, pvp and GNW. You can make a good team out of them, still worth to get them.

But it's up to you whether, which super rare(s) you want to get first i.e. Kurama, Madara, SSasuke, Ay.

SB Ay is pretty strong, search on youtube for reference.

A lot of people were hyped up for this GNW, most of them have completed Kage treasure. Something new, so players would have more varieties and don't always use the same teams over and over.