What is it that makes this route a direttissima? I’m not super familiar with the term.
All 48 peaks on the AMC white mountains 4000-footers¹ list in one continuous trek (no driving/shuttling/etc between trailheads).
¹ this list is outdated vis-a-vis modern mapping and includes at least one peak shorter than 4000 feet (Tecumseh) and omits at least one peak that should qualify per the rules (Guyot), but if the list were updated they would still have completed the direttissima, since they passed over Guyot on the way to the Bonds (dropping Tecumseh could only make the diretissima easier, but I'm not sure it makes much of a difference; it's been a decade or so since I hiked that section of the whites).
As an aside, that day 5 from Wildcat to Cabot is absolutely brutal even if you're fresh, to say nothing of having already covered 180 miles in the previous four days.
It has a lot more overhead than regular forwards mode autodiff because you need to cache values from running the function and refer back to them in reverse order, but the advantage is that for function with many many inputs and very few outputs (i.e. the classic example is calculating the gradient of a scalar function in a high dimensional space like for gradient descent), it is algorithmically more efficient and requires only one pass through the primal function.
On the other hand, traditional forwards mode derivatives are most efficient for functions with very few inputs, but many outputs. It's essentially a duality relationship.