I actually think that it is becoming increasingly more difficult to climb the ranks after the first few thousands. I think it is somewhat problematic for a game trying to attract new players because they start with a gap which is very hard to close.
But there are many many nations whose are far from optimizing their growth and those who are ready to make an effort can climb the ranks and reach nuclear capability in a matter of a few months.
While I see the reason in setting a fixed requirement for nukes (after all, in the real world, what you need to get nuclear weapons does not change over time), CN is not obliged to do this. It has always been "a bonus" (I could not find a better word) for big nations and it is 100% fair to leave it this way. I actually think that a Manhattan Project, in most cases, is self destructive for a nation.
Getting nukes is not the holy grail of CN and, while they are of course very valuable for war, you can do very well without them. Buying a Manhattan Project, IMHO, is wrong for nations who are not very active militarily for a few reasons:
1. Usually, for such nations, the upkeep price of nukes is a big part of their daily income. They could better use it elsewhere.
2. The money spent on the MP itself can help a nation much more if spent on infra.
3. The same for the money spent on buying the nukes for nations this size.
Everybody is entitled to their own opinion, of course, but I feel that people whine too much about how the game is not enough in their favour. The biggest CN nations got there by working hard on optimizing their nations. It is true that age is an advantage, but I cannot see how this can be wrong. Instead of complaining about how hard it is to grow your nation, do what is necessary to make it grow faster.