Yep! Absolutely true, and one of the reasons why Encrypt-then-MAC is the only generic composition method scheme that always provides certain security properties

Yep! Absolutely true, and one of the reasons why Encrypt-then-MAC is the only generic composition method scheme that always provides certain security properties (specifically, security against chosen-ciphertext attacks given that the "encrypt" part is secure against chosen-plaintext attacks and the "MAC" part is secure against forgeries).