The Archdruid loses Wildfire
A ranged spell attack is not necessarily connected to Spellcasting at all. Take the Sun Soul Monk's (Sword Coast Adventurer's Guide) Radiant Sun Bolt for example:
You gain a new attack option that you can use with the Attack action.
This special attack is a ranged spell attack with a range of 30 feet.
You are proficient with it, and you add your Dexterity modifier to its
attack and damage rolls. Its damage is radiant, and its damage die is
a d4. This die changes as you gain monk levels, as shown in the
Martial Arts column of the Monk table.
This is a ranged spell attack, but Monk's get no form of spellcasting and this is not a spell.
The spellcasting section in chapter 10 of the Player's Handbook states that:
Every spell has a level from 0 to 9.
Therefore, simply because it is a ranged spell attack, it is not considered a spell if it does not have a level from 0 to 9. Similarly, Wildfire is not listed as part of the Spellcasting action, and "Wildfire" is not a name possessed by any pre existing spell, it is being specifically created by this feature in the Archdruid's stat block.
Wildfire is an action that the Archdruid can use, and the only thing that "Ranged spell attack" means is that it is using it's spellcasting ability modifier in the calculation of said attack.
What this means is that the many "Spell-like" features in the new book are not spells, even though some of them mimic existing spells, if such a feature does not say "The creature casts X spell" then it is not a spell.