As someone obsessed with the game's lore, I understand that some old lore has been retconned and some of those player cards may have been related to that, but that tree card really was special, as well as the stained glass card.
I loosely theorized that the tree was a sequoia or redwood that came too close to Radianite and grew to an astounding size. The Stained Glass card seemed like a reference to First Light, or maybe to a particular girl with some exceptional radiant powers.
The Haven Formation one was also spectacular, paired with the mystery of the device within. The Radianite explosion card stirred discussion regarding what kind of refining Kingdom is doing to the Radianite to produce the Spike "explosion" versus the explosion depicted in the player card.
I miss them, regardless of their involvement in the current lore; but if I had to pick one, the nameless Tree Card is definitely the most missed.
Edit: Thanks for your contribution to the game's art, and if you're able, send my love to the environment artists!