Range getting picked for mark is why we tend to stick with sending melee up. It is perfectly normal to not kill every soldier up there. DoT everything you can, kill 1-2, rinse repeat. Boomies and spriests are both very OP at DoTing so not bad choices (boomkin can solo as stated before) but if you keep hearing the "I got mark + smash" excuse you need to do something different as that is always going to happen and you can't do much about it. If you get mark, you need to refrain from going into the smash that round and a backup DPS needs to go. You can NOT get smashed + soak a mark, just not gonna happen.
No one should be out of range, because literally everyone should be following around the siegemaker (or in melee/tank case, be moving in front of the siegemaker / the siegemaker is always heading towards the melee group where the bombs will soon be). If anyone gives the "so and so" was out of range excuse again, it's because "so and so" or the healer was not behind the siegemaker like they should be.
Positioning is extremely easy p2... be by the giant siegemaker... GG
And again, the dot on stands ticks HARDER the longer you are up there. You should be jumping down at 30% health, no more, because the dot is about to ramp up and take you down to 0 very quickly. Living is more important than MAYBE killing one more soldier.