Moonfire is pretty pathetic damage.
The initial portion is instant, but the majority of the damage is from the DOT portion over time.
By spamming it, they're doing low damage and wasting a lot of mana.
Which means the mobs are alive a lot longer than they need to be.
That translates into more pounding on the tank and the healer going through mana like crazy.

Wrath spam or Starfire spam, either way is going to increase your kill power dramatically.
For quest NPCs (the mobs you need to kill or remove so you can collect stuff), I found it was 6-7x Wrath to kill things (meaning just slightly more than one volley from five druids).
One Starfire volley (x5 casts) was similar damage to two Wrath volleys (10x casts).

I'm not sure if it is still the case, but at one point Blizzard had acknowledged that Feral Druids were missing a couple tools that they needed for tanking.
They got these in the upper 70s.
Now that it is a Guardian Spec for tanking, I'm not sure if that is still the case.



I did not go the dungeon route, but when I leveled druids they were 5x Feral, and that seemed to be massively overpowered.
They were easily able to kill every mob, along the Zygor quest progression, even (intentionally) forgetting to use the click-this-item to reduce the mobs power.
Only the guy who explodes in Hyjal, unless you run away... could not be overpowered.
For perspective, my 4x Death Knights + 1x Holy Paladin team, wiped in six encounters that the Druids breezed through without even a slight hiccup.

My rotation was a simple one:
#show
/castsequence reset=target Mangle(Cat Form), Rake(Cat Form), Mangle(Cat Form), Mangle(Cat Form), Ferocious Bite(Cat Form)

For tougher mobs I had a different rotation, essentially the same except for alternating finishers:
#show
/castsequence reset=target Mangle(Cat Form), Rake(Cat Form), Mangle(Cat Form), Mangle(Cat Form), Rip(Cat Form), Mangle(Cat Form), Rake(Cat Form), Mangle(Cat Form), Mangle(Cat Form), Ferocious Bite(Cat Form)

It's worth noting, that for questing I basically never got to either finishing move.
10x Mangles, with some Rips... obliterated everything.

The rotation was essentially alternating IWT (with CTM on) and the first castsequence.

As a Feral Druid, sometime fairly early you gain automatic/passive heals when you land a critical hit.
And the critical rate was somewhere around 35-40%, so they each got a heal every 6 seconds or so (the cooldown on the ability).
The act of whacking things in melee, restores a healthy amount of mana; after even a short fight, a previously out-of-mana druid has enough for several casts.
Rejuvenation x5, on 1-2 druids... as needed, then back into cat form is strong heals.
You can even pre-HOT your team, or one Druid only (who while Feral, goes Bear Form just to generate initial threat).

Predatory Swiftness (at 26th), gets you a 20% chance for an instant cast per combo point spent, with a finisher move.
Druids (and Rogues) have an ability where they can often get 2 combo points.
I worked out the math, given a 30% crit rate (my team was always higher crit rate than that), and you had between 97 and 98 percentage chance for your spell to be instant, when you used a finisher (which in the rotation follows four 1-Combo Point manuevers... meaning 80% chance to generate the instant cast, if none of the first four moves failed to generate the extra combo point, and a 100% chance is even one of the four previous moves did).
You basically want to round robin the Predatory Swiftness, tying it to Healing Touch (or Regrowth, if the glyph for that basically gets you +40% critical heals still).
I also had Predatory Swiftness on a separate key, for Nature's Swiftness (which glyphed, was a 100% hit point rez in combat... and powerful as an instant cast).

I don't see Nature's Swiftness.
It seems to be replaced with Ysera's Gift - that's passive pulsing heals to the Druid... or at full health, to an ally (your other Toon).
Nature's Vigil is way down the road, but it provides heals just by killing things.
You can round-robin both of these... tap once or twice, for some heals... spam when the shit hits the fan.