Yes, they can.
Simple reality of event planning: If a customer has hired BOTH you and a band - then the band probably isn't that versatile.

PS: All of the effects and tools built into our DJ controllers are available (and originate) in live performance.
Most bands are hired to perform within a particular range, and the most versatile bands can be cost prohibitive for the general wedding market. That's where
agency comes in.
I've performed live WITH bands - segueing in and out of each other; but that's with 900+ people for something like a major pharmaceutical company - not the personal taste of bride & groom at their wedding.
Bands (musicians) are STILL the better entertainment when properly vetted and evaluated, They also remain the source of what most event DJs play - something DJs take for granted. No matter how well we mix - it's still someone else's creative work we are manipulating..