No problem with the concept of replying too quickly to actual posts but this is something different. It is most likely at the point of replying that you’ll say to yourself “this topic needs splitting”. It certainly should not throw away my hard-typed reason for flagging.
PS. Although one wonders how effective the two nags of replying too fast or not including enough text in a reply are. I suspect most just pause for a few minutes and still reply and we definitely get “…” at the end of short posts.