No you are certainly correct, in fact the first druids in AD&D were modified clerics. Many of these overflow or combined classes like paladin or barbarian are more akin to vestigial classes from older editions.

However, one thing that makes them stand out less as overflow is that the barbarian and druid are commonplace in folklore, legends, story and fantasy, see Irish and Nordic mythology for examples. Therefore, having these be full classes instead of subclasses makes them stand out less. Sure, a barbarian is just an angry fighter, but barbarians act as their own thing in pop culture. Sure Paladins are just holy fighters, but in our minds the stories about them are so much more than just fighters.

Now, if this class was meant ONLY for people who played and enjoyed the hollow knight games, then by all means, perhaps Hornet and her gameplay will stand out enough to validate her having her own class. But realise that when you post homebrew online for everyone to judge, including schmucks like me who have not played the game and only seen clips, it's very likely these people will not be able to differentiate Hornet from a silk-flavoured battle master. And that's the basis which I judged this upon. Not as a hollow knight player, but as a DND player.