There is a difference between "Ливни стали причиной наводнений" and "Причиной наводнений стали ливни".
The first sentence simply says that heavy rains caused floods. The second one assumes that the reader already knows about the floods and says "It was heavy rains that caused the floods".
The Russian sentence "Доктором стал Джон" does not mean "Doctor became John". It implies that there was more than one person who wanted, or could, or was expected (etc.) to become a doctor, but it was John who became one.