It should indeed be the same carrying capacity as the druid herself/himself.
It's just silly otherwise, I've realised that I never shapeshift anymore even though I'm a moon druid...
Well, it doesn't help animal forms are underpowered garbage past lv2 without inheriting your higher AC and you even do more damage in humanoid with Shilellagh while having access to healing and ranged utility on top.
The sheer annoyance of being encumbered when you swap to anything but bear/wolf/deep rothe is just the cherry on top of the awful shapeshift design balancing.
The point of animal form is not that they can fight better than humans.
- The bear gives you 60HP extra and you can taunt enemies so your companions can attack them without fear of damage.
- You can reach some places that are hard to reach otherwise.
- You can concentrate on a spell while you (as bird) watch this from miles away.
If animal form had the AC and damage of humans plus the extra health pool, special abilities and mobility they already have, druids would be totally OP and it makes no sense to play another class.
Prof. Dr. Dr. Mad S. Tist 
