This is more about sealed memories than amnesia, because the seme takes aways the uke's memory. This is the main plot of the story, since the seme's mission is for the uke to remember him.
The amnesia is the plot twist of the story. The seme without memories has a 180° change and we can see how the uke is suffering a lot. I understand is the main plot of the story but the suffering part is dragging a little too much maybe.
The amnesia is a big part of the story but it was refreshing that it has not a bad impact in the main couple dinamic. It was a re-encounter story, so the amnesia was also a way to see how they fell in love again even with the seme's memories gone.
The amnesia is not part of the original plot, is in the side stories. We can see a "new side" of the seme with his memories gone and it was nice that it was not drag a lot creating unnecesary drama.
The uke lost 10 years of memory because he change the future. But is not really a part of the plot, just and after effect.
Tiger's Coming Down