Don't arena "equalize" the stars? Which would mean gnw tenten effectively gained 3 star compared to the main (or the main lost 3) and 1-2 star against most other ninjas.

Tbh, I don't see the aforementioned mabui-tenten-mei team very often. Maybe once a week in masuri. Probably something to do with level and power range. Where I'm at, water immortals are far more common, on average I get 2 or so per masuri, most of which features roshi. So yeah, it is a phase, people will grow out of it.