If not for the Gospel of John, we would think Jesus' ministry lasted one year

According to P. Schaff (The Nicene and Post-Nicene Fathers Second Series Vol. I), "the Synoptic Gospels certainly give the impression that Christ’s public ministry lasted but a single year; and were it not for the additional light which John throws upon the subject, the one year ministry would be universally accepted, as it was by many of the early Fathers,—e.g. Clement of Alexandria, Tertullian, Origen, Lactantius. John, however, expressly mentions three, perhaps four, Passovers, so that Christ’s ministry lasted either two or three years.

Upon comparison of the Synoptists with John, it will be seen that the events which they record are not all comprised within a single year, as Eusebius thought, but that they are scattered over the whole period of his ministry, although confined to his work in Galilee up to the time of his last journey to Judea, six months before his crucifixion. The distinction between John and the Synoptists, as to the events recorded, is therefore rather that of place than of time: but the distinction is not absolute.