The main issue is that from level 2 to 6, the moon druid progression is terribly flat. All the other (sub) classes progression is linear but somehow this one has to suffer through 4 levels where they start as good and end up as either a subpar land druid or a mediocre fighter. This is both not fun and unbalanced.
How is the moon druid progression not linear? They gain new spells at lvl 3 and lvl 5 just like every other druid subclass.
A mediocre fighter? Maybe at lvl 5 when fighters gain extra attack. Until then a Bear druid with Barkskin is not much worse than Lae'zel with her starting armor and a greatsword. Every fighter/barbarian/paladin will always outperform a moon druid in the later levels in melee because of magical items and feats anyway.
A subpar land druid? At lvl 5 land druids know 4 more spells than moon druids. Are they all useful? (are they even all implemented yet? Mountain should gain access to Lightning Bolt and Meld into Stone at lvl 5 for example) Why should a moon druid care about spells they can't cast in wild shape anyway? If you play a moon druid and you only cast during combat of course you are gonna be worse than a subclass that uses its subclass feature. Meanwhile why should you use wild shape as a land druid before you use all your spellslots in combat? A land druid should not start their first turn in combat by going into wildshape as their only action for that turn.
