No Hindu disputes that the mantras in the Samhita part of the Vedas are direct revelations by Rishis.
But what about the texts of the Brahmanas, Aranyakas, and Upanishads? These don't seem to be revealed by Rishis.
The Srimad Bhagavata Purana also says that Vedavyasa just divided the Samhita portion of the Vedas only at the end of the Dwapara yuga:
The most powerful and intelligent Vyāsadeva called four of his disciples, O brāhmaṇa, and entrusted to each of them one of these four saṁhitās.
This implies that the Brahmanas, Aranyakas, and Upanishads were authored in the Kali Yuga.
The Srimad Bhagavata Purana also says that the people of Kali Yuga will have diminished intellectual faculties:
Verse 47: Observing that people in general were diminished in their life span, strength and intelligence by the influence of time, great sages took inspiration from the Personality of Godhead sitting within their hearts and systematically divided the Vedas.
This makes sense because the Brahmanas serve as a manual for Yajnas, and the Aranyakas and Upanishads talk about the symbolism of Yajnas and the nature of Brahman and moksha, respectively, and manuals and commentaries are only needed when people are not intelligent enough to understand the original source itself, which are the Samhitas in this case.
