Yeah. They really need to start adding magic items mundanes can use to protect against this garbage. Oh but wait, mages would be able to detect the items. Sorry mundanes, you're screwed. One newbie mage with a low level stunbolt and astral perception could punk an invisible Solid Snake, at range. Hell a newbie mage with the same setup could nail any mundane prime-super runner that wasn't a mage themselves. Big bad assassin Riser? Bah, astral perception, stunbolt. Supermerc Picador? Bah, astral perception, stunbolt.

I thought that while in astral perception the Mages are supposed to be in Astral themselves and thus are only allowed to cast spells at dual-natured or astral target.

You sure can see them but you wont be able to cast anything at them.

No you can cast at targets on EITHER the material, or the astral, and if you're willing to multicast, I 'think' you might be able to hit both at the same time, but don't quote me on that.

It takes a Simple Action to shift
one’s perception from the astral to the physical, and another to
shift it back again (it is not possible to see both at the same time,
though almost everything in physical space is reflected on the
astral, albeit without detail).