Milos’ sickness was due to him being genetically sensitive to lightning aether, in an environment suffused with it. Since the scions have no such condition, and the environment isn’t as bad as the 13th no scales were needed. Alisaie even mentions that while the porxie is able to realign his aether it can’t to anything about his sensitivity and he can quite easily relapse.

And no, magics of the same element as an overaspected shard don’t mutate, the ones of the voidsent didn’t, so why would lightning in Alexandria.