The Blackwater is generally used to refer to the river, not the bay. So I don't think the granted tract of land for Daemon was anywhere near the Hook.
As for the location of the invasion, we don't really know why they landed there of all places since we know relatively little of the rebellion. Possible explanations could be:
I personally like to imagine an even more than usual snarky grandpa Aegor attempting to do a Hail Mary (Hail Maiden?) in an attempt to purge the realm of some Targaryens before he kicks the bucket.
As for the location of the invasion, we don't really know why they landed there of all places since we know relatively little of the rebellion. Possible explanations could be:
- The Hook is the closest you can get to Kingslanding from Tyrosh without getting uncomfortably close to Driftmark and Dragonstone. They might not have wanted to risk conflict with the Valeryon fleet or where forced to land there when they found the way to Kingslanding was blocked. It's just a walk through the forest and crossing the river from there.
- House Massey is the first house you come across from your starting point in Tyrosh that aided Bloodraven during the second Blackfyre rebellion. They might have wanted to retaliate against the houses that chose sides against them during earlier rebellions.
- They might have expected to find support there, or expected to gain support once they set up a strong vantage point on the Hook. Landing in the Crownlands has the benefit of not pissing of any of the lords paramount for invading their land. The Hook had once been part of the Stormlands, maybe they hoped to grant it to the Baratheons in exchange for their aid.
- Bittersteel might have become a bit impatient in his quest to defeat the Targaryens and just said "fuck it, it's got to be now" because he was 64 at this point and he wasn't about to get any younger. Grandpa Aegor would die just a few years after the Battle of the Wendwater during a skirmish.
I personally like to imagine an even more than usual snarky grandpa Aegor attempting to do a Hail Mary (Hail Maiden?) in an attempt to purge the realm of some Targaryens before he kicks the bucket.