I actually have no problems with a Wiccan Priestess being an arcane practioner. (Hey, some of my best friends are Druish!

) It in some ways can be viewed as a form of theurgy, lit. god working - Witch is her religion, priestess is her
job. Leading the faithful, but relying on her own powers rather than those of her gods, or using her own power to coax, cajole, or bully her gods into performing what she needs done.
The difference between a witch and a cleric might be akin to the difference between a rabbi and a cohen. I have run games where
most of the priesthood would be deemed experts, some wizards, and a slightly greater number of clerics than wizards. (Most of the great universities were started by the church, and historically one of the best known 'wizards' was Albertus Magnus - who is a saint on the Orthodox calendar. Wizardry in that world began in the universities, so most wizards have at least a grounding in theology.)
For what it is worth,
most of my friends are pagans of one brand or another, while I squaek by being a Unitarian/Universalist. (Motto: We don't know the answers, but the questions are nifty.)
And of course modern and ancient religions are silly - they are made up of
people! (And U/U is among the silliest, trust me on this...)
The Auld Grump