I disagree with that, just like I think Wizards and Sorcerers both deserve to exist. Sure, they both use arcane magic, both use the same spell slot progression, have fairly similar spell lists, have the same hit dice, have the same weapon and armor proficiencies, and many other features and flavoring that make them overlap, but are different classes. The same thing applies to Divine Soul Sorcerers, Celestial Warlocks and Clerics, as well as Scout Rogues and Rangers.
You are so quick to throw up all these things, that I don't think you are considering my point at all.
Because, obviously both the Sorcerer and the Wizard should exist, none of their mechanicaly stuff even needs to be mentioned. Sorcerers are born with great power. Wizards study and learn to wield great power. That is a big thematic difference.
Druids worship nature and nature gods.... Nature clerics worship nature and nature gods.... They appear, thematically, identical.
Druids being reffered to as an "old faith" implies that it is a religious sect, they are worshiping, but stop and think about it as describing two people standing in front of you.
Who is that? Oh, that is a Druid, a member of the Old Religion, he worships Obad-Hai, the Lord of the Forest.
Okay, who is that? Oh, that is a cleric, he worships Obad-Hai, the Lord of the Forest.
Are there "Old Faiths" for all the gods? What do you call an "old faith" worshipper of Pelor, or Kord? Are they also Druids? Why does Obad-Hai want a difference between his "old faith" and his new faith? Did he just not update the OS?
None of it makes sense. It doesn't make sense that Obad-Hai would want to have two different types of worship, but no other deity would, it makes no sense that if his worship changed he wouldn't pressure the old sect to adjust to the new beliefs, none of it really works thematically.
Maybe other people can make it work, but for me, it makes far more sense that worshipping Nature is fundamentally different than worshipping a God. It makes far more sense to not have a God of Nature at all, or if you do, they only have Druids, not clerics. They are working in a fundamentally different manner than the cleric does.
Druids don't have to worship any deities, and neither do Clerics in 5e. I talked about this in this
post. Long story short, druids don't draw power from deities, clerics don't have to, but druids embody nature while clerics worship it.
Sure, nobody has to worship any gods. But that doesn't change anything. A cleric worships the philosophical idea of nature.... doesn't a Druid as well?
You say that Druids "embody" nature. So, is there a class that "embodies" other religious concepts, like Love, War, or Strength?
If Clerics worship nature, and Druids "embody" nature, would a cleric worship a Druid? That would make a Druid something Clerics would strive to emulate, because they are closer to Nature than the Cleric is. The Cleric is an outsider, while the Druid is an insider.
And we are back to the same problem. What purpose do we have in showing both concepts?
And, again, I'm not saying anyone is wrong or bad by using them both. I personally don't like it. I personally see this disconnect, and see no reason to have Nature Clerics. I personally find it more intriguing to separate Nature from the Gods, I also did the same with Arcane magic. There are no gods of the Arcane or Nature in my games. They are different paths.