Actually, by the time Rogue got to APEX S3 the Korean Scene had already tried and pretty much discarded triple DPS dive in favor of D.Va, and for a while at that. It's one of the reasons they were able to handle Rogue relatively easily even though they were a great team.
Those also happened to be the future winner and runners-up of the tournament so that's another big factor.
One thing to note is that Pros of any region will eventually all end up using what would be considered the optimal meta with some variations so the notion that one region is "copying" another is a bit odd.
As far as I can see from watching EU/NA, CN and KR, it seems that KR is typically slower to adopt "new metas" if they're not forced to. One possibility is that they're unwilling to use it in tournament play until they're confident that they can be as effective as possible on them.
It's hard to say without access to scrim data on all regions simultaneously to see who is using what. The question of if they've ever come up with their own thing or if they've just been copying other regions is a bit of an odd one in and of itself since in the end it doesn't really matter.
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