I've not been part of designing systems at that scale (yet!) but isn't event sourcing kinda envisioned for just these kinds of problems in mind? Like you would

I've not been part of designing systems at that scale (yet!) but isn't event sourcing kinda envisioned for just these kinds of problems in mind? Like you would have all of that "core" data as Kafka topics and can safely interact with them without affecting the core services? I know the answer is always "legacy" and "its been designed that way from the beginning" but I was wondering what do you think would have been the right way to design something like this to mitigate risk of current / future problems?