I see why garv's lineup works.

Consider those facts:

1) Darui do not boost anyone in round 4 and is not boosted by water main, while haku does.

2) Haku is 5 stars while darui usually is 3 star.

3) It's true that darui lands during the first 3 rounds 6 140% standard attacks and in round 4 1 standard at 100%, so you land a total of 940% with standards, but haku here lands 1 in round 2, 2 in round 3 and 1 in round 4 but he does it with a 210% boost + 10% more stats, so is like if that boost went to 230%. 230%*4 = 920%. so more or less the damage from standards is comparable in terms of boosts, but haku is slightly higher in truth because his standard attack is high scaling, while darui's is medium scaling. The damage from mystery too is comparable, both are low scaling. So on darui side there is the pro of 4 low scaling 10 combos chases, but on haku side there is the +40% boost in round 4 for all the damage landed by utakata and main mysteries and chases and by main clone, that in the case of utakata chase is something astronomical with 3 hokage supports, since his chase is one of the highest scaling chases that are out there, thing that obviously don't work as well in pvp because resistance and damage reduction highly depower it, but against an enemy with 0 resistance...