he is no less clever than his elder brother. 그는 형만큼 똑똑하다. (그래도 형이 더 똑똑)
he is no more clever than his elder brother. 그는 형처럼 똑똑하지 않다. ( 둘다 똑똑하진 않다)
모 자료에서 위와 같이 설명하는 것을 보았습니다.

혹시 아래와 같은 논리로 보는 것은 어떠한지요?

he is no less clever than his elder brother.
→ he is as clever as his elder brother or more. (동생이 더 똑똑하다는 어감이 되야 하지 않을지...?)

he is no more clever than his elder brother.
→ he is as clever as his elder brother or less. (둘 다 똑똑하지 않다...라는 어감이 있는건지...?)