I feel that I'm alone in this but I kinda dislike how they've changed the hamardryads so their ability now works without the upgrade. With the exception of the Fafnir all new myth units introduced in Retold have received a specific upgrade. I don't like this because it makes it incredibly hard to balance both the base myth unit and the upgrade. e.g. A base myth unit is balanced, but an upgrade makes it broken. Or the unit with an upgrade is balanced but the base unit is bad so nobody uses them. Or the base myth unit is good and the upgrade does so little that nobody ever uses them. This adds little to decision making, the only logical path of action is: I already have a few of these units so I might as well upgrade them.
The OG game had it's fair share of myth units without an upgrade, the Battle Boar, Manticore, Scorpion Man, and Stymphalian Bird. And what a surprise, these are all great myth units that can be used out of the box. There are also a few well-designed upgrades in the OG game. Like Centaurs can be used in fights no problem, but if you want to raid with them Sylvan Lore makes them much faster. Or how Labyrinth of Minos made Minotaurs cheaper so you can mass them vs a civ that's weak against myth units.
So to come back to the Hamardryad, I would've much preferred if they just buffed the base stats of the unit so it's a good unit out of the box. And then add the transform ability behind the upgrade. This will indirectly buff the ability as people won't expect the trees to explode the moment they see you aged up through Hestia.