When John first sees four multi-eyed living creatures, they are in the midst of the heavenly throne (Revelation 4:6-7). They lead the heavenly worship (4:8), but they don’t seem to act at all on earth.
Then the Lamb takes the throne, and becomes the throne (5:6), displacing the creatures. And suddenly they are empowered to summon and speak. As the Lamb breaks the first four seals of the scroll, the creatures take turns summoning horses.
Lamb and lion act together to bring the white horse; lamb and ox to bring the red; lamb and man to summon the black horse; and lamb and eagle to call out the green horse.
In the Old Covenant, God worked through angels. The Lamb has taken the throne and the scroll, but Revelation still operates in the Old Covenant order, so cherub and Lamb work together to bring the judgments.
Eventually the task of the cherubim will eventually be handed over to human beings. Then a human voice like thunder will call out the horsemen of heaven.