I don't have the PHB. Does it actually say anything to the effect of "your animal companion does nothing unless you use your <resource> to direct it"? Because if it doesn't I think it's an unwarranted leap to assume it can't act.
If it does say that it is ridiculous. So I can tame an animal and have it follow me around making 2 or more attacks per round entirely on his own while I go about my business...but if I'm a ranger and decide to form an animal companion bond with it, it becomes a mindless automaton that can't act unless I'm specifically telling it what to do? Yeah, right.
Now, it makes sense if you are summoning a creature and you have to exert your will to keep it under control that it might only be able to act as your direct it with your action (especially if the creature has a stronger combat presence than you do), but not for an animal companion.
About rangers in general, I wouldn't consider DPR or combat presence as a sole indication of class balance. If it has more out of combat utility than a fighter, paladin, or barbarian (and again, I don't know if it does) it must have less of a combat presence in order to be balanced.
The 3rd level class ability shouldn't increase damage by too much. Going by a Fighter, it should only increase your damage by a bit less than 5%. Can anyone think of a way to have the pet acting independently but not increasing the Ranger's damage by more than ~5% at level 3?
My player had a 3rd level Ranger (human colossus hunter) with a Heavy Crossbow and the Crossbow Expert feat tonight. A lot of damage.
One is a 3rd level spell and is compared against Fireball, the other is a 3rd level class feature and is compared with critting on 19. Fireball deals 8d6 damage in a big radius. Critting on 19 adds less than 5% to your DPR.Yes the spell requires concentration...but it's just an example. IF the concern is having the animal companion attack for free unbalances the class, why do summoned creatures not follow the same rules? the spell also scales by level, but the ranger is still stuck with a 1/4 CR pet. so no lions, tigers or bears...ever.
Oh my!so no lions, tigers or bears...

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.