Was Hooke close to developing a physical system of gravity on the same level as Newton. looking at Luka Trkanjec's post on Quora, he insists that Newton was quite overrated in this regard, and that Hooke was close to developing a system of gravity with the inverse square law
Hooke was not close (as far as we can judge from his surviving work) to what Newton accomplished. Yes, he conjectured the inverse square law. He understood correctly some simple qualitative features of the motion under this law. He probably performed some simple experiments suggesting these features. And he proposed to Newton to prove that the inverse square law would imply Kepler laws. This is known from his correspondence with Newton. It is clear from Hooke's letter that he could not prove this himself, and he recognizes this.
Hooke was not a mathematician, and it was clearly far beyond his power to prove mathematically that the inverse square law implies Kepler laws. The conjecture itself was widely discussed at that time, not only by Hooke. Sir Christopher Wren even proposed a prize for proving it. But nobody could do this except Newton.
If you glance at the contents of Newton's Principia, you will see that it contains VERY MUCH more than a proof of Kepler laws from the law of attraction. It contains a comprehensive theory, which essentially lays the ground for mathematical physics. Nothing even close to this can be attributed to any author among Newton's contemporaries. And Newton's contemporaries understood this very well.
It is another, different thing, that Newton was not fair to many of his contemporaries, and did not give them credit which they deserved. But for the theory of gravitation he did much more than they all combined.
In Newton's own words (from a letter to Halley):
Mathematicians that find out, settle & do all the business must content themselves with being nothing but dry calculators & drudges & another that does nothing but pretend & grasp at all things must carry away all the invention as well of those that were to follow him as of those that went before.
This is harsh with respect to Hooke, but correct.