To follow God's word in the Quran would be to follow the messenger

The Quran states explicitly that the messenger's duty was only "to convey the message (29:18)," and he said nothing on his own as his own sayings (69:44).

It states that the message that the messenger conveyed was the Quran only (42:52 & 14:52 & 69:44).

Therefore, to follow God's words in the Quran

would be to follow the messenger, (4:80), as the words of the Quran is the messenger's speech (69:40).

It also claims to be the Qawl or the speech of the messenger (69:40).

The Quran claims that it contains answers to ALL relevant questions (25:33) and contains the best explanation (Tafseer) of itself (25:33 & 2:159).

The Quran claims to be the Hukm or commandments of God, according to which humankind is to be judged (5:48).

It also states that it is the law/way with which God sent the messenger (45:18 & 42:13).

Who would know best on how to talk to humankind but their creator?

Therefore, it makes no sense to say that outside sources better explain God's word.