I am not the right person to judge that and I will be glad for further comments from English natives, but I think frightened is more about fear that happens just now, not a regular one - similar to terrified.
I have now found this example:
He is a stern master. The boys are all afraid of / scared of him. (More natural than ‘The boys are all frightened of him.’) https://www.englishgrammar.org/afraid-frightened-scared/