65% def mooded roshi on a HP tile can easily die round 1 to any form of lighting blitz, be it the old mb blitz or newer cloud blitz, due to those teams having mostly tai/nin mixed attacks. He also dies to mabui 1010 on round 1 if a standard attack combo go off on him thanks to all the tai/nin mix attacks and pure nin attacks he receive. This kind of roshi is almost certainly dead at start of round 2 if facing an opposing hidan roshi team; while a hp mooded one will survive comfortably.

HP mood is there so that your roshi do survive to round 2, where he can break potential barrier and take significantly less damage in return, or receive healing/shielding support from your team. 65% hp let him eat quite a bit more hits than 65% def in early rounds. Def mood only works well against pure tai attacks.. which is not that common, as most high damaging attacks in round 1/2 are tain/nin mixed or pure nin.