Conveying revelation is one angelic duty, but not their only one. Scriptural accounts also describe worship, glorification, protection, recording of deeds, and other assigned functions. What unites these actions is fulfilling divine command, not independent sovereignty.
Describing an angel's task must not suggest that the angel possesses a self-sufficient power outside divine authority. Being entrusted with a function and being its autonomous ultimate cause are different claims.
This establishes the relation between belief in angels and divine oneness: honoring angels does not divide or dilute God's sovereignty.