The follower’s Quranic recitation and saying Ameen are separate legal questions. In Hanafi doctrine the imam’s recitation covers the follower, who nevertheless says Ameen after al-Fatihah.
Shafi‘i law separately requires al-Fatihah from the follower. The source statement that the follower says Ameen is not itself proof that the follower must recite al-Fatihah independently.