I disagree with you entirely. "Lowest-hanging fruit" isn't the same as "low-hanging fruit". The phrase "low-hanging fruit" does specifically mean that the solution is easy, in a vacuum - the fruits are "low", which is not relative to the other fruits or the height of the tree, but relative to the ground.
>the obvious or easy things that can be most readily done or dealt with in achieving success or making progress toward an objective
So not only can it be "obvious" rather than "easy", it is also in the context of "achieving success or making progress toward an objective". There is nothing in the definition that requires either this specific step or the overall goal to be easy.
