Druids are a second-tier class IIRC, cleric and wizard are first-tier.
Druids are firmly rooted in tier 1.
Well actually neither, it depends on what kind of spells the druid in question have. For all we know, the Druid may have picked up only useless spells, like Goodberries or something and be tier 5.
But they pick their spells every morning, from all that are available. It's not like a sorcerer/bard/favored soul where you can screw the character up by picking bad spells-known. It's as flexible as a
wizard cleric. Except that the list of spells isn't so expansive... But there are things druids can do, like healing and summoning certain specific useful creatures, that aren't available to arcane magic.
Besides that, they get
3/4 BAB (like a rogue!) and some weapon proficiencies
no penalty for casting in armor (they START with medium proficiency, and the only caveat is that the armor can't be metal. But ironwood crafting armor is just fine)
2 more skill point per level than wizards
They can turn into a bird and fly, or a fish and swim, or a bear and maul you. At level 10 or so they can be like this all day.
Later they can become an earth elemental and glide underground, or an air elemental and fly 100ft perfectly, well you get the idea
Oh, and their animal companion (twice as powerful as the ranger's). Like the evil druid in OotS said: I have class features more powerful than you!
... And, wow, they actually get slightly more spells per day than a wizard! Wizards seem to cap at 4 spells per day of each level. Druids get up to 5 (6 for level 0).
And unlike a wizard who prepared the wrong spells, druids can spontaneously cast Summon Nature's Ally. Which includes things like unicorns for healing/curing, and elementals for various utilities.
... OH! And wizards have to actually find or research their spells, and carry them around in a BOOK, whereas druids (like clerics) just get them all from a short meditation every morning.
The only thing that balances this is that arcane magic list has many spells that have no druid version. But the druid spell list is pretty damn good too! It has elemental blasting, plant-based utilities, healing, buffing, walls... Most notably lacks illusions and force attacks.
I know what I'm going to do with my STEM degree!
Haha, this is great!