Can you show me an example of where you might want the first post to be replaced?
When merging two topics, I would expect the person doing the merging to select the one they want as “primary” as the target “existing topic”. If it happens that the older topic is that one, chronological order will naturally be preserved. If you choose the newer topic, it seems logical that you’d do that because you want to preserve the topic introduction. Does that… make sense?