When it comes to this, I think there’s actually a few different ways to go about it - like you said, mages draw from different sources, different styles. But there’s also different ways to going about the same art - such as the difference between the Warriors of each culture, or Human/Stormwind/Kirin Tor Magic versus Night Elven/Highborne Arcane Magic, versus Silvermoon, versus Suramar, et cetera et cetera.
When it comes to the Harvest Witches, Druids, and more, a good thread to look at I’d say is actually the Kul Tiran thornspeakers for druids - since the original settlers of Kul Tiras were originally from Gilneas, it makes sense that they brought some traditions with them, including the Harvest Witch form that eventually emerged into Thornspeaking.
As for where Gilnean Druids fall - I’d say somewhere squarely in the middle. They didn’t have death-speaking witch-druids carving runes of death, but still attuned themselves to nature spirits, and did take refuge with the Night Elves who recognized their potential as druids and taught those who were willing to learn. Somewhere between the ‘Glory of the Eternal Life of the Elves’ and ‘Balance of Death and Life’ - with maybe a little bit of Goldrinn/Moon focus there if you want to aim towards all the lasers.
A bit of supplemental reading - “Thornspeakers RP Guide” by Grumdil, over on WrA! Thornspeakers RP Guide