But do the defenses extend to Harry? Or just the cell block.
Mostly, it depends.
The island seems to have limited initiative, and most of the high-powered defenses need the Warden to activate them.
Harry at Skin Game (after an extended period exploring the island and its powers) is a very-different Warden than Harry at Turn Coat (after he did the Sanctum invocation)... IIRC, TC-Harry didn't even understand that he was the "Warden" of a "Prison!"
So, the Warden is a key component of the island's defenses.
It'd be kind of silly to leave the Warden undefended, or without the extra defenses the Island
could provide. Harry thought he was bluffing; the SC-members & Wardens in Turn Coat... and he
was bluffing them, in that he was largely ignorant of all that power; he was just relying on the advantage of the Intellectus (and likely some halfassed "just in case" ideas about tapping the ley lines).
SG-Harry
wouldn't have been bluffing ... on the island, it's likely he really could have taken a bunch of Warden hardcases and SC members, all at once.