In academia, does the amount of material that one has to learn diminish as time progresses? From my own point of view, the first year of a PhD is heavily packed with new information, theory, techniques, conventions, experimental abilities, etc. Let us call all these elements "material". This new material required a lot of effort which I felt as a heavy burden in comparison to my master thesis or any previous academic experience. This burden was also complemented by requirements of the PI, funding entities, bureaucracy, etc.

The second year was also heavily packed with new and deeper material. But the burden of acquiring this new material was in my opinion, lower. This perception of a lower burden can be due to better learning methods, more experience, a more relaxed view on life, due to actually less new "material" to deal with.

I felt as if I had to sustain the same first year burden for several years, I would eventually collapse. And even though the second year burden was lower, I would not be able to continually perform at a good level under such burden.

Is there any point in an academic's life where the burden diminishes? I enjoy learning new stuff, carrying out new experiments and acquiring new skills. But the rate at which I feel this is necessary during a PhD is for me too high and I would not like to have a permanent life under this burden.

Just to be clear, it is obvious that in Academia it is necessary to acquire and master new "material" continuously. My question focuses on the "rate", if it makes sense.
The first paper I read took two months to process.
Now, I can skim through two papers for breakfast. It is not that you get more material to read, but rather you get much more efficient at skipping things you know or recognize as unimportant. 

It comes with practice - try reading papers and books, and think about what are the important parts. Learn to identify the 'meat' and which techniques are used. Also, you'll notice that instead of learning 'the stuff', it is about cataloging and storing meta-information about where to find 'the stuff' once you really need it.

After a while, you realize that most of the new papers you read, you only need the gist of it, in order to reference it. Comparably few papers need to be read and understood in paragraph-by-paragraph detail.