From what I can tell it’s a bit of a mix still, however the coronavirus may have slowed down some plans as travel between Perth and Bunbury wasn’t possible for a while.
You’re correct, most of Hit’s networked connect is coming out of Perth now, from hit92.9’s second studio. For breakfast, Michelle is still in Bunbury at least some of the time.
Triple M is still mainly from Bunbury - most of those announcers are long term Bunbury residents so are less likely to want to move. However breakfast for remote WA (branded as Triple M North West) hosted by Ray Love is coming from Perth.
SCA only have 4 on air studios in Perth, and previously workdays and breakfast would use different studios to allow the breakfast team to use the studios after their show for pre-recording content as required, so I’d imagine it’s pretty crowded in there at the moment.