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?
if that was the only issue then summoned creatures should need commanding.
At level 5 we can use conjure animals to get 8 1/4 CR animals (same as a companion). They can all attack for free, admittedly without the prof bonuses. Now this spell can also be cast by rangers, so how come summoned animals (all 8 of them) attacking without using actions is ok, but an animal companion must use an action. If the action granted the prof bonus to attack and damage, fair enough, or just to choose a new target, but for every attack it doesn't make sense.
Level 5 ranger - attack my pet. panther attacks on +7 to hit, 1d6+5 damage...
Level 5 druid - summons 8 panthers. on the next round all 8 panthers attack, +4 to hit, 1d6+2 damage (x8), plus the druid gets to do an attack as well.
Level 9 ranger - attack my pet. panther attacks on +8 to hit, 1d6+6 damage...And the ranger can use his extra attack to attack himself!! But the companion is still only a panther (with 36hp) and can only use one attack until Lvl11. Ranger can now cast conjure animals but...
Level 9 druid - casts conjure animal to summons 16 panthers as above, or 4 brown bears. on the next round if using bears, bite +5 , 1d8+4 damage AND claw +5, 2d6+4 damage...each.
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.