There is definitely something qualitatively different about weeks/months long tasks.
It reminds me of the difference between a fresh college graduate and an engineer with 10 years of experience. There are many really smart and talented college graduates.
But, while I am struggling to articulate exactly why, I know that when I was a fresh graduate, despite my talent and ambition, I would have failed miserably at delivering some of the projects that I now routinely deliver over time periods of ~1.5 years.
I think LLM's are really good at emulating the types of things I might say are the types of things that would make someone successful at this if I were to write it down in a couple paragraphs, or an article, or maybe even a book.
But... knowing those things as written by others just would not quite cut it. Learning at those time scales is just very different than what we're good at training LLM's to do.
A college graduate is in many ways infinitely more capable than a LLM. Yet there are a great many tasks that you just can't give an intern if you want them to be successful.
There are at least half a dozen different 1000-page manuals that one must reference to do a bare bones approach at my job. And there are dozens of different constituents, and many thousands of design parameters I must adhere to. Fundamentally, all of these things often are in conflict and it is my job to sort out the conflicts and come up with the best compromise. It's... really hard to do. Knowing what to bend so that other requirements may be kept rock solid, who to negotiate with for different compromises needed, which fights to fight, and what a "good" design looks like between alternatives that all seem to mostly meet the requirements. Its a very complicated chess game where it's hopelessly impossible to brute force but you must see the patterns along the way that will point you like sign posts into a good position in the end game.
The way we currently train LLM's will not get us there.
Until an LLM can take things in it's context window, assess them for importance, dismiss what doesn't work or turns out to be wrong, completely dismiss everything it knows when the right new paradigm comes up, and then permanently alter its decision making by incorporating all of that information in an intelligent way, it just won't be a replacment for a human being.