When it comes to describing something as "overbuilt", it's generally understood to mean that it was constructed with a greater degree of strength and durability than what was actually needed. However, if you're looking for synonyms that could be used to describe something as even more overbuilt than usual, you could consider alternatives like "heavily fortified", "excessively sturdy", "exceptionally robust", "hugely reinforced", or "incredibly solid". These terms all imply a level of construction that far surpasses what is required, indicating an excessive focus on strength and durability that might not be entirely necessary.