because flame Nola has a 25s skill cooldown, which does not match with Nan Yin's 60s skill cooldown. If I am using flame Nola, I would have to either spend 10s doing low damage to fill the blank, or leave Nan Yin's skill non active for 15s. I tested both and they end up doing less damage than simply using physical Nola.
Nola's discharge only does damage and provide no buff, and have a long animation. It is better to skip it when you don't need to wait for skill cooldown. Edit: Nola's discharge was not skipped in the Nola/Nan Yin/Plotti Rotation If you mean Nan Yin's discharge, it does not do much without any burn related weapons like Feise. You could swap Nola's discharge with Nan Yin's but it doesn't change much on the damage output.