First of all, there are not 'three Mysteries', there are FIFTEEN.
Second, the Rosary is as Christological as ANY prayer EVER; what part of all of the Mysteries from the Annunciation (of CHRIST'S ADVENT) to the Coronation (OF THE MOTHER OF CHRIST) could POSSIBLY be misconstrued as less than Christ-centered?
Second, the Rosary IS NOT FIVE DECADES. IT"S TEN.
ONE HUNDRED AND FIFTY PRAYERS, REPRESENTING THE ONE HUNDRED AND FIFTY PSALMS WHICH ARE PRAYED IN THE DIVINE OFFICE.
Monastic brothers and sisters used to pray EVERY Psalm EVERY DAY. Things have changed, of course, because people's time constraints have increased, and, of course, due to the Modernist influence of the Conciliar heretics. They are more than happy to let people pray dumbed-down, shorter devotions and 'meditate' on 'new mysteries' which are, as has been said, an affront to the heavenly perfection of Our Lady's gift.
Honestly... how on earth can you POSSIBLY look at what the Rosary IS, and always HAS BEEN, and see its former SIGNIFICANT and CENTRAL place in the devotional life of Holy Church, and then look at today's compromised sham of religion and not WEEP?
It's simply because you've thrown out the depth of meaning, historical pride of place and ESSENTIAL disciplinary character of Our Lady's Psalter in favor of your lax, ecuмenical New-Age foolishness.