Truth be told? personal preference.
Thats where I began to dislike the plot.
I was depressed with the plot of the series from shortly after they blew up the Yeerk pool all the way till the end.
Im no one to assume the right of judgement, but personally Id've rather seen the cube get lost to Tom, the pool blow up, a more all out war, some goverment guys in on it, but in the end;
A; Tom sacrifice his life to kill the Visser One's Yeerk and Save Alloram and the Animorphs.
B; the Animorphs all survive
C; the whole thing get covered up as part of the terms negotiated between the Animorphs, the Andalite Government and the US Government.
D; Jake frees his parents.
E; their hometown is largely un-scathed
F; no publicity. at all.
G; some kind of transferance, where another group of kids say finds the morphing cube which say was assumed lost in the destruction of say the bladeship.
Something of that nature.
But if you were going to give them a chance to do things different, that would be the best time, because the destruction of the Yeerk pool was the focal point for the rest of the series events.
