Example of Evil surmisings
So you could claim that people that say that someone cannot be saved by the gospel of John could be into evil surmisings.
The gospel is mentioned already in Matthew. Christ preaches the gospel in Matthew.
So by not consenting to that the wholesome words of the lord Jesus christ are enough for eternal salvation they are evil surmising.
(John 20:30-31 [KJV])  And many other signs truly did Jesus in the presence of his disciples, which are not written in this book:  But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.
We can see in Jon 20:30-31 that the book of John is about getting people eternally saved.
John 1:12 KJV But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name: