Is there a consensus or mainstream view among historians re: whether or not the US "had" to drop the atomic bombs on Japan at the end of WW2, to avoid a much bloodier land invasion? Or, how has the historiography around this question evolved over the years?

While more can always be said, this section of our FAQ may be of some interest, in particular this answer and this answer, both by /u/restricteddata. One thing that I think would be worth pointing out is that the idea that the US was making an "invade or bomb" decision in the summer of 1945 is a myth, specifically having been created in the postwar period to retroactively justify the use of the bombs.