General

mm.vs.wh in mobbing

basic breakdown, I will be using normal(6) xbow with no boosted speed atm, pierce will use 540 ms charge time as that is unaffected by any booster, all mob skills will be added a 55% dmg to each hit due to riding mastery and wild beast

pierce: 540 ms charge time+870 ms firing = 1410 ms doing 1150% dmg with 1.2x multiplier as it goes through each monster
crossroad: 1320 ms cast time, dealing 570%+55% dmg = 625% dmg with stun
sonicboom: 1980 ms cast time, dealing 700%+55% = 755% dmg with stun
flash lane: cast time 2970 ms, total dmg of 10 arrows+explosion 1850%+(55%*11) = 2455% dmg
you can compare wild shot, obviously not made for big amounts of mob anyways, feel free to do it on your own, 120 ms each arrow 200%

now let's compare
pierce.vs.crossroad
1410/1320 = 107% rounded
1.07 x 625% = 668.75% dmg

crossroad = out

sonic boom comparison:
well you tell me, do I need math here, when pierce has a shorter time, larger range and do more dmg, I can tell you crossroad outdo sonic boom though

flash lane:
2970/1410 = 211% rounded

1150% x 2.11 = 2426% dmg, where pierce has a 1.2x multiplier on each monsters it passes

but realistically flash lane can't really be beat, it's larger range+15 monsters, only thing is really 30 second cooldown.

conclusion:
pierce dps/dpm > mobbing dps/dpm potential of any wld hunter skills, yes this includes flash lane with 2 mobs or more, however it is starting from 6+ mobs that flash lane will start to gain more power. but basically 30 sec cooldown is 30 sec cooldown.