My friend @shadowweirdo has a theory that the reason why Varian looks so different from Quirin is because of the opal. We see Quirin get blasted by the opal’s magic in the flashback. (s2e1) It could be entirely plausible to say that the opal’s magic contributed to Varian’s physical features.
ie: black hair / blue streak , pale skin , blue eyes ; all of which look like a humanized version of the rocks.
The rocks are destructive, and so is Varian. Barring his status as the s1 villain aside, he’s clumsy, has a penchant for bad luck, and somehow, someway his inventions tend to destroy everything around him. Even the biggest rock formation in Corona turned up smack dab in the middle of Varian’s house of all places. The rocks completely destroyed Old Corona without a trigger.
More than anywhere else, they grew in Varian’s village, so much so that the entire populace had to evacuate.
Not to mention that Varian speaks FOR the rocks in Rapunzel’s prophetic dreams. Each time she dreams about the rocks, Varian is there. The rocks follow him, react along with him, and his anger towards her mirrors that of the rocks’ destruction as they moved towards Corona proper.
Varian is also the only one (besides Adira, who we KNOW is from the Dark Kingdom and connected to the rocks and opal) to tell Rapunzel to “Face her Destiny”, and we all know that Rapunzel’s destiny ties in directly to the rocks.
In essence, because of the traces of opal magic passed down from Quirin to Varian, thus effecting Varian’s physical appearance, the rocks see Varian as “one of them”. They use his visage to speak to Rapunzel, creating yet another mirror between Varian and Rapunzel: the sun and the moon.