My first to 80 team was/is 1x Prot Pally with 3x Elem Shammy and 1x dual-spec Elem/Resto Shammy.
The team could take solo elites 2-3 levels above them, while leveling up.
I've not raided with them, as a group, although the pally and one Elem shammy has a bunch of Naxx gear now.

I've got 5x Balance Druids at 60, which I'd like to level at some point.
I've got 5x Disc. Priest at 60, which I'd also like to level at some point.

Prior to boxing, I had leveled several toons to 70th, single boxing.
Two of these joined the first team, Pally and Shammies.
But five more have sat at low 70's or 70, through WotLK.

I recently decided to level these "orphans" as a mixed team.
75 Feral Druid, 74 Disc Priest, 73 Elem Shaman, 70 Demo Warlock, 70 Marks Hunter.
To mix it up, this team was going to do instances instead of questing.
One boxing, a Feral druid clicking each move as needed is a strong option.
Unfortunately, I cannot seem to come up with a castsequence which holds threat.
Consistently, the Priest takes threat on secondary targets from heals.
Often enough to be irritating, the Shaman (chain lightning) and Hunter (multi shot) take aggro too.
Utgarde Keep (level 71 recommended level) was *FAR* easier with 70 Pally/Shammies.

My Druid's click sequence was: Enrage (1 per fight), Demoralizing Roar every 12 seconds, and looping Mangle, Swipe, Maul, Mangle, Swipe, Lacerate when Roar was not firing. I had the glyph for Maul to hit additional targets.

Priest was precasting Prayer of Mending and PW: Shield, with a Renew early. Used Pain Suppression and heals manually. Had both Target=TargetTargetTarget (targted Druid always) heals and G-Keys for specific character heals.

Hunter was Hunter's Mark, Serpent Sting and Misdirection once per fight. Arcane Shot, Chimera Shot, Multi Shot as cooldowns permitted, with Steady Shot when everything else was on cooldown.

Shaman was Elemental Mastery when available, Flame Shock every 18 seconds, Chain Lightning every 4.5 seconds and Lightning Bolt when others were not on cooldown.

Warlock was Demonic Empowerment when available, Agony, Corruption, Immolate as they expired, Lifetap every 40 seconds (for the glyph bonus), and S.Bolt spam when others were on cooldown or waiting to be recast.

The dps was good with the mixed group.
Boxing the druid, I couldn't build secondary threat nearly as well as the Pally.

Pally would Consecrate early, and have Holy Shield up all the time. Initial threat would have them hit the Pally, and Holy Shield was enough threat from their own attacks, for the shammies to never take aggro. Boxing the Druid has nothing of this sort.

No comparison between the two.
Level 70 Pallies+Shammies had a much easier time (fewer deaths too), then a 75 tank, 74 healer...

Have respec'd the mixed team, after a few dozen attempts to tweak their macro's.
The mixed team is now...
Balance Druid, Shadow Priest, BM Hunter, Demo Lock, Elem Shaman...
And leveling via Pew-Pew in BG's.