If players didn't like the idea behind the Arboreans (nature and earth), why vote it so highly?
Bringing in one of the other voted themes might rectify a critic or two (such as the Magisterium, whose focus is on nations with multiple high level priests which probably cuts across many paths, have to look into it) though I am sort of saving the other highly voted choices for game 3, trying to avoid as many conflicts as I can. With the power of Collegium Arcanum, and the evil of Regnum Inferorum (reminds me, I need to add a fire path to them), a divine theme sounds best in game 3.
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IMPERATOR·CAESAR·LVCIVS·SEPTIMIVS·SEVERVS·PERTINAX·AVGVSTVS·PIVS
Be harmonious, enrich the soldiers, and scorn all other men.
-Emperor Septimius Severus, to his sons shortly before his death, quoted in Dio Cassius (77.15.2).