Mmmm, I would say that Higurashi isn’t solvable in the traditional sense. (Umineko Spoilers) This is because unlike Umineko, Higurashi does not follow the rules of Knox, nor is it designed to be a fair play whodunnit mystery.
As someone who is familiar with the mystery genre, there are a couple main reasons why Higurashi wouldn’t be considered ‘fair play’, though it doesn’t really need to since its more of a modern mystery rather than a Golden Age Detective mystery, which is a rather specific subset of the mystery genre.
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First and foremost, it violates the rules of Knox, who is a very influential writer when it comes to fair play whodunnits. The most notable violation I can think of is of the 4th rule of his which states “No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.” This is notably violated with both Hinamizawa syndrome and the vaccine for it. Both of these are not things the reader could reasonably be expected to have knowledge of the properties of beforehand, which violates this law in spirit.
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It does not seem to give all the clues necessary to reach the who and why in due time before the reveal, in my opinion. Again, this is not strictly necessary as it is of a different genre than the fair play whodunnit, being a modern mystery and all, but it would be a mistake to say that it is something that should be referred to as ‘solvable’ for that very reason.
Theres probably more I am not thinking of off the top of my head, but while yes it probably is fairly easy to suspect Takano, I sure did rather early on in fact, its far harder to -prove- her involvement before the story really gives you the information rather outright due to how everything is set up in my opinion.