I was sat at the hold in BRU one night as an A320 diverted in with a cargo hold smoke warning.
Listening and watching; the crew in that incident were absolutely explicit that they wanted an inspection and feedback from the fire crew before deciding the next move. The AFRS having looked at the aircraft recommended evacuation so that's what happened.
We heard later that when the hold was opened there was no fire or smoke and it was a dodgy sensor.
These decisions are not simple or easy for anyone either on the flight deck or in the AFRS who are trying to peer through an aluminum skin riddled with pipes wiring and ducts.
I've always thought the German system of the AFRS having a set of widebody fire truck type steps was sensible. It would allow for a rapid but controlled de-planing.