It is good to read their assessments, however between the possibility and the factual is a gap. Would a anti-Chinese Taiwan be a problem if you want to invade Japan? Yes. However the power to project is there already, as Taiwan is tiny compared to the strategical ports China got. The point is not if it would make stuff easier, but if Taiwan is a necessary condition - which it isn't (though would make it a load more easy, after building much more port sites).