Maybe is because gnw kankuro mystery add a bad status while sage naruto one doesn't do. The ai thinks is better to depower them than to try to direct kill them.

I don't know but what i know for sure is that my mei is placed after tenten gnw but if, for any reason, on round 3 mei still have to cast her mystery (because mabui wasn't able to give her the previous round the chakra) she is the one that uses her mystery in tenten place. Doesn't matter where she is placed on the battlefield nor the order of placement. Her mystery gets priority over gnw tenten one. And there could be only two reasons to explain this: 1) mei's one adds ignition debuff or 2) mei's one could hit targets even in other lineups in comparison with gnw tenten's that can hit only one lineup. I think the ai is scripted in the latter way because the ai the program runs was made for ranked battles/tis/wanteds and just reused for spacetime.