They create their own backing to suit the arrangement they are creating, so as to make sure it fits what they want, and doesn’t sound like anybody else. (Over the years they build up their own unique backing library) Many also play their own backing live.

Multipads as used on an arranger were on workstations/synths long before arrangers got them. (They just weren’t called Multipads)

Apart from Korg (Which have a version of the TC Helicon vocal harmoniser) the rest fall well short of the quality required for a top notch performance, which is why a separate unit is used to get the best quality.

Anything else

Bill