The prefix ‘mi-’ is not used for the present simple of ‘daashtan’ داشتن , right?

For the most part, yes, but for prefixal verbs and some compound verbs, ‘mi-’ is used. For example:

bar-midaaram برمی‌دارم ‘I pick up’ (from bar-daashtan برداشتن ) // vaa-midaare وامی‌داره ‘it makes [someone do something]’ (from vaa-daashtanواداشتن ) // negah midaare نگه‌می‌داره ‘s/he keeps’ (from negah daashtan نگه‌داشتن ) // paas midaarandپاس‌می‌دارند ‘they protect’ [formal] (from paas daashtanپاس‌داشتن ).