I have a similar impression as you but I also found this quote illuminating:

"I never read the Pricipia Mathematica; almost no one has. You know it's not really traditional in Physics to go back and read the original papers of the great people before us. I'll confess I've never read Einstein's original papers on Relativity even though I've written a textbook on Relativity. In Physics the idea is it's the ideas matter, not their original presentation."

"Newton's original presentation of this stuff in the Principia - number one, it was in Latin (laughs). It took a while for it to be translated into English and number two, he was apparently afraid of using all of the new mathematical techniques he invented. So he tried very hard to only use existing mathematical techniques so people would believe him, so people would accept it right away.

"Subrahmanyan Chandrasekhar, who is a great 20th century astrophysicist, actually wrote a version of the Principia Mathematica for the common reader. If you ever want to know what Newton was actually up to in the in his great masterwork the Principia I would advise not buying either the original Latin or English but buying Chandrasekhar's explanation of what was going on."

- Sean Carroll The Biggest Ideas in The Universe pt 2 @15:55 (youtube)

After getting my degree in Philosophy everyone would always ask me about Plato and Socrates... but, at the time, I had not read anything about either of them - my studies were focussed on logic and philosophy of the mind and cognition. At the time I felt silly admitting that, but I have since read a lot of antique philosophy and the majority if it is the same - a bunch of babbling with a few sprinklings of ingenious ideas. If you want to comprehend the immense ideas from great historical philosophers you are much better off reading primers or summaries with the high-points than reading the entire original texts.

I checked out Newton’s Principia in graduate school. It’s incomprehensible because it heavily uses geometric arguments that basically no one uses these days. It’s hard stuff and looks nothing like modern calculus. I think it was L’Hospital’s book that actually looks very similar to modern-day calculus.

Leibniz’ work, from what little I’ve seen is a bit more readable, mainly because he was concerned with the conceptual-ness of it all.

Feynman, for a challenge, decided to do things the old-school geometric way, and he reported it was “damn hard”.

In contrast, Einstein on (special) relativity is excellent. I haven't revisited them since my undergrad days, but I remember being surprised by just how clear and direct the original papers were. Much easier to understand than many modern attempts! The terminology is a bit outdated in places (such as, if I'm remembering right, what you call the mass term γ m₀), but that's not hard to deal with.

Yea, Einstein’s papers and a lot of those early 20th century physics papers are surprisingly quite readable, even for a moderate layman such as myself. Because of this, I must say I find Carroll’s claim that he’s never read one of Einstein’s relativity papers a bit dubious.

Dirac’s paper on magnetic monopoles contains a rather beautiful and general introduction on progress in physics. I highly recommend it.

http://users.physik.fu-berlin.de/~kleinert/files/dirac1931.p...

This makes me wonder how important or useful rigorous / axiomatic arguments for intuitively true “facts” are. As far as applications are concerned, it seems like the physicist’s math (what Feynman calls Babylonian math as opposed to the axiomatic Greek math) works well enough, while rigorization often trails by decades or centuries (as in the case of calculus).

That could be true with other fields too, I remember reading that amongst serious economics students there is the practice of reading Adam Smith to this day.

Yes, these days Goldstein and Lanczos might be more apposite