Ranger: Literally useless due to dumb-as-a-brick pet mechanics, inability to attack moving targets, heavy emphasis on single-target dee-pee-ess which is weak, lack of stun breaks with reasonable cooldowns, extreme lack of condition removal unless traited for, etc. They do, however, have Healing Spring (the best water field in the game, shortbow thieves and hammer guardians take high advantage of this) and decent access to AoE immobilize/fear via hound, Entangle and wolf respectively. But ultimately, they bring nothing to the table that another class can't do better and with less hassle. And yet they're the target for an upcoming damage nerf across-all-formats (if ANet's track record indicates).
End-of-the-day, a random ranger might not be helping his team to full potential and a random team is unlikely to take full advantage of it. This doesn't mean "useless", but simply underutilized. They aren't meta, because your typical meta-build ranger attempts to do things a ranger isn't really suited well for (ranged high-DPS just doesn't exist).
Healing Spring - As you've said, one of the best water fields in the game. Properly traited, this provides the entire team with Permanent-Regen, Vigor with high up-time, and Condition removal too! Ranger's also have a blast finisher via Drake pets adding in AOE burst heals on top of the regen effect, in addition to whatever blast/leap finishes the team can execute.
Tanking - With evade utility, Vigor, Natural Vigor, Protect on Evade, 30% Evade on Auto-Attack, 1000+ Passive Healing per second, channeled blocking, and stone signet - a Ranger can make a damn amazing tank class.
AOE crowd control. You've listed Hound, Entangle, Wolf. Add in Muddy Terrain, Spike Traps, Frost Traps, and Barrage. Rangers have insane amounts of AOE immobilize/cripple. As far as I'm aware, this level of redundant crowd control effects is unique and unmatchable.
DPS - In point of fact, Ranger's have two weapons that are AOE on auto-attack. Traited, a bow ranger has pierce on auto attack. Drake pets do cleave, can AOE, and it's a separate set of cleave/AOE targets from the Ranger. There is no reason except for poor positioning and poor weapon selection that a ranger would not be hitting multiple targets.
The Pet - This brings risk mitigation to the team. Pets can wade into a crowd of mobs, not draw a single bit of attention to itself, and pull a target. If the pet gets spiked and dies, that's a whole set of heavy hitting skills that the pulled group have on recharge and the pet is instant rez. Furthermore, the pet is immune to the vast majority of environmental effects - Fractal Blizzard / AC's spike traps / etc - and can be healed/prot'ed from any range.
Additionally, the pet allows a ranger to split his attention between multiple targets, taking a moderate DPS hit rather than committing an entire party member for control purposes - for examples:
- DPS the CoF slave driver, while at the same time pet-tanking the flame effigy
- CoF bubbles encounter, the Ranger can occupy a bubble and pet-DPS the controller at the same time
- Urban Fractal - pet-tanking the squire while attacking the captain
- TA worms, the pet can be set to auto-guard mode to clear blossoms, freeing the team to focus on the boss
- TA end-boss, the pet can take all three spirits into a corner, allowing everyone else to concentrate on the nightmare tree
- Fractal Maw - the pet can be deployed across the map to attack any target, so that the team can fight without becoming overextended from support
Damage Support - If a Warrior can reach 25 might on his own, guardian/mesmer can make +20 might team-wide, then more might doesn't make the damage numbers go up. Frost spirit is a multiplicative bonus on top of the +30% damage you get from Might. Longbow's almost always up-time 10 stack of vulnerability is another +10% (and pierces to multiple targets...). The two skills together basically let you over-cap beyond the 25 stacks of +damage, allowing access to +40-50% damage ranges.
And of course... rangers have AOE revive, pet revive & quickness boosted rez.