The way to be informed about the requirements for salvation is to read all the verses that talk about it, one verse is not enough, or even 2 verses. John 3:16 is good in informing us we need to believe Jesus is the Son of God, but it is not enough. It is just partial information, you need more to get the whole picture. It does not conflict or disagree with other verses, but it gives us only part of the information. Heresies like Christian Science and the Unification Church also believe Jesus is the Son of God, yet they are not saved, because they do not meet other requirements. The Unification Church believes Jesus is a Christ, a Messiah, yet we need to believe he is THE Christ (John 20:31, 1 John 5:1). Christian Science believes Jesus did not die, yet we need to believe he died for our sins (1 Cor. 15:3), and that God raised him from the dead (Rom. 10:9). Christian Science also believes that flesh is not real, yet we have to believe Jesus came in the flesh (2 John 7). So both are false gospels.
We need to believe all that, and also repent (for example Acts 2:38). So we cannot rely on one verse alone, but get all the verses on the topic to get the whole picture.