I have a Druid Player in my campaign right now, let me touch on the multitude of problems he's had with his character.
- Trackless step may cover the trail of the character (scent is arguable) but it however does not cover the tracks of the party. This ability can be emulated by a 1st level druid/ranger spell, and is arguably better.
- Yes, druids are immune to Poison. Shall we talk about Paladins? Monks perhaps? Poisons are strong yes, but they are the one class that is immune. If there is a druid in the party that is immune to poisons, use them on the other 3 to 4 people that are with him. Just cause the druid is immune doesn't mean the entire party is.
- On the note of Wild Shape, let's take a "full caster" Human druid level 5. Str 10 Dex 14 Con 12 Int 10 Wis 18 Cha 10. 15 point-buy, not optimized but rounded out. You turn into ANY medium creature and only gain +2 Str, +2 AC, and an alternative movement or sense. If you turn into a small creature you only gain +2 Dex, +2 AC, +1 to Attack, -1 to CMB/CMD, and an alternative movement or sense. I'm sorry, but losing your armor (assuming it's not Wild) and gaining what? +2 Str? That is not a huge advantage in the slightest.
- Summoning creatures is strong, especially Nature's Ally. But compare it to a Conjurer with Augment Summoning, buffing his summons and party with haste, all while invisible. The druid pales in comparison.
- The Animal Companion (Depending on when it's size upgrade is) is Decent 1-5, Good 6-10, then falls behind after that. It is never as good as a well played front-line melee combatant. The Summoner's Eidolon will trump any animal companion any day.
- On the action argument. Easily 3+ characters actions are a bit much. In a situation with no enemies using crowd control, you get 3. Druid casts a spell/attacks, mediocre animal companion attacks, mediocre summon attacks. A wizard has 2, more powerful, actions (stronger spell, summoned creature) and a fighter usually does the same amount of damage the companion and summoned creature do.
Overall, you are giving the druid FAR too much credit. Is it a powerful class in the hands of a good player, yes. Are all the classes powerful in the hands of a good player, yes. Part of the responsibility of being a DM is making the game dynamic and interesting for the players. Sometimes you play to their strengths, other times you play around them. I have had to do this with all of my players, you just need to know how to play around them to create a more challenging environment instead of just throwing a big monster at them with poison
