No, simply not true. There were sizable cities in Ganha, for example, 3, 500 year ago.
Again, simply not true. South Africa, for example, was never decolonised, while colonisation of much of West Papua only began in the 1970s and continues to this day.
In what way are they similar, beyond containing some Black people?
Africa was largely populated by small metal-working “village kingdoms” comprising larger tribal groups. The people almost all had long-term experience with rival expansionist kingdoms. There were significant trade routes with the rest of the world going back to at least the bronze age.
In contrast parts of New guinea were populated by Indonesians who were at about the same level as Africa. However the vast majority of it was occupied by stone-age villages with limited trade routes and only highly informal clan connections. The highest population densities were almost completely isolated from the rest of the world.
Really, there is no commonality on their histories that I can see that could not equally be applied to anywhere outside Europe.
The question is utterly meaningless.
The problem you are going to have is that neither “Sub-Sharan Africa” nor “New Guinea” are countries. They are regions with multiple independent nations and foreign dependencies and states. A such it is simply going to be impossible to find useful statics on the regions as a whole.
The second problem is that the regions are neither heterogeneous nor equal in size. So any figures you can find are useless for comparison purposes. As a hypothetical example, how do you propose to account for the fact that Africa contains, say, 18 functional, democratic nations, 15 less-functional dictatorships or corrupt democracies and 19 despotic basket cases and 7 nations in a state of civil war, while New guinea contains 1 democratic nation, 1 less functional nation and one complete basket case? Do those figures suggest that Africa is better or worse than New Guinea?
As I said, the question is utterly meaningless.
Anecdotally I would say that Africa is well ahead of New Guinea. While Africa has many troubled regions, it also has numerous perfectly functional democracies that are largely safe, crime free and advancing such as Botswana. In contrast none of the New Guinean states are functionally democratic and none of them are safe. But as I noted above, there is simply no sensible way to compare the two regions.