What makes a TH7 layout hold
Mass Dragon attacks are the classic Town Hall 7 strategy, so the position of the air defenses matters more than at almost any other level. Layouts that keep them deep inside and away from each other force Dragons to path through more defenses before reaching them.
Town Hall 7 also unlocks the Barbarian King and Dark Elixir, which is why many TH7 hybrid layouts protect the Dark Elixir storage in the centre.