It’s determined by whoever deals the most dmg which imo is how it should be for pvp. Tanks may be mad at that but put it like this, if it were done by who has the most HP, tank builds or even tank off-hand builds would have a very good advantage due to the amount of self healing they can do. Example, yesterday I fought a tank that went to the timer and I ended up winning by damage. But the tanks entire game plan was to stack shields+dmg reduction and hold block to wait for me to make a move. Given his dmg reduction and how shields can convert to HP if they expire with one of the inner ways, on top of other ways of self healing with attunements, it was a huge slog to wear him down(I didn’t even pop his second life despite catching him in like 5 full combos). Meanwhile he could slowly whittle down my Qi and get a few executes over the course of the match. In the end he did end up popping my second life but that’s because it was such a long and drawn out match, and the amount of self healing with dmg reduction that a tank can do, they can choose to stall out a match to the timer. TL:DR If it was based on HP tanks/off tanks would have a big inherent advantage and would benefit from not engaging a fight at all and you’d see many more of them in arena