Optimal groups are comprised of a tank, a healer, crowd control, and 3 DPS classes.
Regarding your group makeup beyond that
- CC -- Bards are actively benefitting the group regardless if caster or melee. An Enchanter has limited buffing potential, but also excels on an unmatched level at crowd control.
- Healer -- Cleric can 100% rez on occasion, 96% in combat, and give some healthy HP buffs. Shamans are more versatile and provide sufficient healing. I have no opinions on Druid - perhaps someone else could chime in on their preference.
- Tank -- SK is the GOAT, Paladins are a good alternative, most have suggested that warriors mainly shine in raids, but I find them to be effective with a properly equipped group.
- DPS -- DPS has a lot of options. Characters like beastlords bring a lot of value to groups. Where-as Zerker/Rogue don't contribute to the rest of the group but they consume from others like the beastlord/bard in a way that really shines. Classes like a necro can deal high amounts of damage, but it takes them time to get going. Synergies and auras should be taken into consideration - every class gets a synergy, that synergy plays a role in proping up the entire group. Not all classes get auras, but they can be beneficial to the group as a whole. For both of these things that means stacking two of the same class into a group can negatively impact the entire groups potential because the effects of Synergy stacking would be nil or negligable, and the auras do not stack to create a more powerful aura.
A long touted ideal group makeup is Shd, Shm, Brd, Bst, Ber, Rog
But mixing and matching based on the above information is fine as well to create another optimized variant.
You already have Shd, ___, ___, Bst, Ber, ___ of that makeup. Adding a bard would put you to 4 of the 6.
Shd, ???, Brd, Bst, Ber, Wiz, Rng - No healer? This is not an ideal group makeup.
Consider replacing the Ber with a healer - I say the Ber because they're the only non caster. Bst provides benefit to all the casters, Shd can use Beza for mana (probably going to need it for the wiz mana pool vacuum), Bard benefits the entire group on multiple fronts and provides your CC.
This is assuming wiz/rng are set in stone.