I'm on the side that Druids are pretty OP and sits up near the top of the 5E class hierachy, but I do want to chime in to clarify a few things.
Let's add some nuance to the propaganda shall we?
Multiclass dip level 1 Barbarian, or level 1 Monk for Unarmored Defense, and you add CON or WIS modifiers to unarmored AC in any shape. A lowish level Dire Wolf/Monk would have AC 18-19 (assuming 18-20 WIS). An Earth Elemental wildshape (level 10-11), would have 17 AC base + 4 from Barbarian dip or +5 for Monk dip (20 WIS) for AC 21-22 total. Clearly we are not talking about crushingly low AC, but rather strong AC for a Druid who cares enough to strengthen his wild shapes.
When you wildshape as a Monk/Druid or Barbarian/Druid, you can choose to either apply your unarmored defense (with the DEX/CON stats of the wildshaped form) or, use the creatures natural armor. So high-dex wildshapes (i.e. Air Elemental) with monk unarmored defense would be the way to go to maximize AC in wildshape (but you can't use that with shields in humanoid form).
This ruling is explained in the official rules answer here:
https://dnd.wizards.com/articles/features/rules-answers-january-2016Here are some ways to calculate your base AC:
Unarmored: 10 + your Dexterity modifier.
Armored: Use the AC entry for the armor you’re wearing (see PH, 145). For example, in leather armor, you calculate your AC as 11 + your Dexterity modifier, and in chain mail, your AC is simply 16.
Unarmored Defense (Barbarian): 10 + your Dexterity modifier + your Constitution modifier.
Unarmored Defense (Monk): 10 + your Dexterity modifier + your Wisdom modifier.
Draconic Resilience (Sorcerer): 13 + your Dexterity modifier.
Natural Armor: 10 + your Dexterity modifier + your natural armor bonus. This is a calculation method typically used only by monsters and NPCs, although it is also relevant to a druid or another character who assumes a form that has natural armor.
These methods—along with any others that give you a formula for calculating your AC—are mutually exclusive; you can benefit from only one at a time. If you have access to more than one, you pick which one to use. For example, if you’re a sorcerer/monk, you can use either Unarmored Defense or Draconic Resilience, not both. Similarly, a druid/barbarian who transforms into a beast form that has natural armor can use either the beast’s natural armor or Unarmored Defense (you aren’t considered to be wearing armor with natural armor).
5. Their caster form is probably going to have middling AC too. Medium armor... But they can't wear metal. That means no mail or half-plate or what have you. Hide is the best armor they can manage and it is only 12+. So assuming optimized Dex and a shield they're sitting at only 16AC. Nothing ground breaking.
Barkskin (level 2 spell that can be up infinitely assuming it has the Hex/Hunter's Mark treatment) + shield = AC 18...even assuming NEGATIVE DEX modifier.
While Barkskin + shield does indeed offer a druid decent AC, it does use and cost a concentration slot.
With a +3 starting CON modifier, until you can get Warcaster, you have a 70% success for the base DC10 concentration checks. It's far from terrible, but hardly a guarantee over a course of a fight (a single casting of level 1 magic missile will likely end your concentration).
And more than any other caster, a druid needs their concentration slot - their spell list is particularly concentration heavy (because they want you to be able to use it with wildshape), especially if you want to be dealing damage. Flaming Sphere, Call Lightning, Heat Metal, Spike Growth, everything takes concentration
6. Speaking of AC, being a druid doesn't mean you can totally dump Dex or Con. You need Con to maintain concentration on spells when not in beast form and you need Dex to make sure your caster form's AC isn't abysmal, as you'll likely get knocked out of form at least occasionally. Likely while surrounded by enemies. Strength is an obvious dump stat, but what full caster can't safely dump strength and still be good?
This is at best commonality for all caster, for virtually all non-casters, and not really a weakness at all. In reality though, a Druid has more freedom to dump just about *any* physical stat as wild shape physical stats overrides the Druid's while also having access to Barkskin spell. Having lowish AC (which they arguably don't have) after being knocked out of beast form is again not really much of a weakness. To help further with concentration checks: A level 1 dip into Barbarian would also add Constitution proficiency, while Enhance Ability/Bear's Endurance spell would add Constitution advantage (and more health), or grab Resilient feat.
You'll need to start as a Barbarian to gain CON proficiency, which isn't a terrible idea (you'll lose your WIS proficiency but gain CON, which is an equal trade IMO). This is intentional, otherwise multiclassing would be too overpowered. Also, the Resilience (Stat) feat would be close to useless.
There is also a trade off to multiclassing. It isn't always a the clear better choice to multiclass Monk or Barbarian for a few extra points of AC.
- Firstly, you need a 13 STR to multiclass into (or out of) Barbarian - it's not an impossible price to pay, but it is stats you're taking away from DEX and CON.
- Secondly, you're delaying access to level 3 spells and wildshape progression - which is a huge power spike for most casters, including Druids.
On Multiclassing Rules:
https://roll20.net/compendium/dnd5e/Character%20Advancement#content
