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If my memory serves me right, I finished "Brave People" at the end of November. A significant portion of the battles there take place when we are defending the castle. Hence, Mephala's skill is needed to withstand the castle's attacks. It can also be completed with Orrin, but it will be much more difficult.
The difference in time is that when playing "for yourself," you spend time checking the editor, prospector, testing the map, etc., while on a stream, even though the streamer should do preparation and tests before the stream, they still don't dwell on analyzing the prospector and editor, instead focusing on some active actions. Therefore, very often on a stream, it's just a simple accumulation of strength, rather than outsmarting the enemy.
These timeframes are more likely due to the fact that the streamer doesn't know or practice tactics that are well-known to most players of average and higher levels: teleporting bears, depleting the ammunition of ranged units, etc., and instead simply tries to break through a superior enemy head-on and, by simply defending, accumulates strength (videos by Richard Chen or (and) Dandy, Rossekavalier on metatactics can be helpful).