Except that no Gmail lists are sorted by subject. Messages are joined into conversations by subject (but not always*), but they are sorted by date. Conversations are ordered by the date of the latest message in the Inbox and by the date of the earliest message elsewhere.
* To complicate that further, messages with the same subject that arrive/depart within a small time frame are gathered into a conversation then if more are sent/received later, they can form a separate conversation. There is no published definition of how short or long the time spans are and if the first few messages are spaced well apart, then later messages can be quite far apart, even days, and still be joined whereas if the first few messages are close together (say minutes), then later messages with the same subject even on the same day might form a separate conversation.
There is obviously a quite complex heuristic algorithm in place to make the conversation decision which is why, IMHO, Google are going to want to tag messages for rejoining rather than try to apply that algorithm every time the view is switched back. It must be very deflating to the programmers who came up with this scheme to learn that so many people want to turn it off.