In part 2, I covered the main tank's role in the PK bomb group. His job is to protect his group from incoming damage and increase the outgoing damage of the DPS in the group.
In part 3, I'm going to cover what I consider the key to this group working. This person's skill will make or break the group. He is the melee focus. He finishes the job, spiking down targets that the bombers have been softening up.
When the melee focus is going in for the kill, the target has already been taking a good amount of damage and has a few DoTs ticking on him from our bombers. He just gives the extra push to knock them over. The ideal candidate for this job has very high front loaded damage. He doesn't have to wait for a mechanic to build up to be 100% effective. You can take a DPS spec tank or an actual melee DPS for this role. The DPS spec tank won't do as much damage as the melee DPS, but the trade-off is the second guard and challenge for the group.
That leaves 2 classes standing in front of the rest, the White Lion (for the more aggressive group) and the Swordmaster (for the more defensive group). That isn't to say a Witch Hunter, Slayer, or Ironbreaker can't do the job. I'll take a good Witch Hunter, Slayer, or Ironbreaker over an average White Lion or Swordmaster for this role, but given equal skill, I'm taking the White Lion or Swordmaster first. The other 3 classes have to build up a mechanic to be 100% and the melee focus is just going in for quick kills.
The SM's burst tool is Ether Dance. The nice thing about Ether Dance is it's base damage is extremely high, on the level of a melee DPS's on each hit. It only gets half stat contribution, so it's damage is largely dependent on your weapon DPS. With 950 strength, 220 melee power, and a 79.8 DPS weapon, I've hit a taunted target for 1200 crits on Ether Dance. That would be almost 1500 with a royal insignia 101.5 DPS weapon. Without any crits, that's still 800 damage x 5 ticks for 4000 damage in 3 seconds. That's my suicide spec with a Knight around to buff and debuff for me though. I just wanted to show the potential damage without having to wait for a long build time. Granted, any true melee DPS class will do more damage, but the reason to take the SM over a melee DPS is for extra defensive abilities he brings the group.
I was the melee focus for this group. The BWs still got most of the damage, but I still put out respectable damage given all the AoE they were throwing around.
The White Lion is preferred since he has his damage mainly front loaded. His big hitting abilities are on a 5s or 10s recast instead of relying on a mechanic to build up. The White Lion is especially recommended if the main tank is a SM. The tactic the White Lion will want is Lionheart. It changes Lion's Fury by removing the Curse requirement, dropping it's AP cost to 20 instead of 35, and doubling it's base damage. Lion's Fury has a 5s recast and does spirit damage. So when the SM is using Heaven's Blade, Wrath of Hoeth, and Whispering Wind in group with a White Lion using Lionheart, the results are quite pleasing. I've had that ability critical for 2.1k before playing as a RR33 White Lion. Imagine spamming that for 20 AP a hit. I can only imagine what a high renown White Lion can do under those circumstances.
This small change to what most players consider to be the traditional bomb group makes it deadly. You've seen the groups that use staggers to take out the healers then assist train the front line down. This minor change to the bomb group uses bombers to cause the effect of neutralizing the healers much like a stagger would while still applying damage to help the melee focus kill targets much like an assist train does. It's the same proven, winning strategy as the stagger, assist train using different tools. Without the melee focus, it's just not the same. Try it out. I think you'll like the results.