I'm thinking either EB warlock playing battlefield pinball (push/pull), or a druid.

For warlock patrons, it sounds like the most setting-appropriate are either Celestial or one of the Undead/Undying types, with Genies as a secondary since there is a Genasi presence. Is that correct? I'll probably go with Talisman boon to help whoever is on the front line.

As far as druids, what's the area around the city like? There's obviously ocean, and ice, but for all that there's an "arctic druid" I don't really see how that matches up well with "nature priest." Sit and become one with the cold? So I'm thinking there would need to be some wilder areas where actually plants and animals grow to key off of, or substantial fields and herds, in order to have something that goes with the thematically incoherent druid.

There's also my druid on the warlock chassis idea, but that would be off DND Beyond, and you didn't say homebrew was allowed.