How do I bathroom / kitchen / extension? etc.

Filling in chasing is not an onerous task, I found it quite relaxing!?
Bonding is easy to mix and use, just build it up with a couple of coats if deep followed by easyfill then tourpret fine surface filler.
It is time consuming but a lot of that is drying time so done in between other jobs.
I wouldn’t expect an electrician to do this, ours used drywall adhesive on the ceiling chases as it goes off quick and rock hard. Was the tool for the job as the chase was not deep as concrete so hard and needed to secure the cable up as the nails in the cable clips were not holding.