Ark and Nexus constructed too fast?

One of the things that has bothered me about the arks and the nexus is there construction, or how fast they were built. Now we know that the ark Hyperion is 1.7 km long, and the nexus is about 15 km long. we an assume that the other arks are the same size. i believe that there is no way the could have been built in the 10 years from the start of the project to launch with its access  to only private benefactors.

Before i get to my issues, let me give some context through comparisons to other ships and stations in the mass effect universe. the largest ship the alliance ever built was the SSV Aconcagua dreadnought at 1km and took 3 years to build. the largest ship built by any of the council races is of course the Asari destiny accession at 2km, and we dont know how long it took to build that ship.  there ships that bigger such as the Qurian live ships 2.817  km long, but we know that the qurians re purpose and recycle ships, so their live ships could be built and worked apon over decades, maybe longer. Since we only know how long one of these take to be built ( the SSV Aconcagua) we can compare that to the arks. Now the Nexus is abit easier to compare because there only one thing we can compare the Nexus to: the Crucible.  you could say the citadel, but we have no idea how long the reapers took to build the citadel, and anything else such as the geth station or the any other station because we dont know long it took for them to be built. So the crucible is the closest thing we can compare it too. the crucible is about 10 km long and took from the start of the reaper war to the end to be built, so about 6 months. 

with that context out of the way, the arks compared to our alliance dreadnought is .7 km longer, and the arks are way more advanced than our dreadnought. we dont know what type of armament and armor the arks, but we do know the arks have to keep together and being operable for over 600 years at ftl speeds, support 20,000 people in cyrostatsis in the arks (in comparison the destiny Ascension had a crew of 10,000), and then support any colony efforts after that 600 year journey.  Not to mention that the Arks has experimental hydrogen engines that were years ahead of its time, especially compared to any other naval star ship at the time minus the Normandy. To add to the arks case, the arks were designed and built to have the idea in mind that they could not go to a space dock to get major repairs for over 600 years, so they had to be built with much higher quality than the dreadnought. dreadnoughts could easily take more punishment and have more firepower. but at longest that dreadnought would be in service for 100 years, with in comparison constant repairs in space docks. With  that being said if the alliance supported the initiative i do believe they could have built a ark in three years. however the alliance didnt support the initiative, only private benefactors did. who these groups were we dont know, but there is no way it could have been at the same level as the alliance military industrial complex. and even if only the initiative made the arks one at a time at a rate of 1 every three years, it would have taken 12 years to build the arks alone (ill get to the nexus later). So realistically it would have to be on every race to build their own arks, which would be difficult without help from the council. that being said i dont believe that they could have built an ark in 3 years, at shortest it would take at minimum 5 to 6 years to be built each, and then they would have 5 to 4 years to test the arks. But thats assuming if each species built their own ark, and thats the best case scenerio. if only the initiative was building them, there is no way they could have been built in time.

Then we have the Nexus. now the case can be said that the crucible is not only more complicated and advanced than the nexus, but also took only 6 months to be built. but that was only done with the help from everything the galaxy could offer under the threat of the reapers, which is not fair to compare to the nexus. the nexus was built in a time of relative peace and only had private benefactors to give it resources. now i know the nexus wasnt complete in the milky way, but the part that was built was 15 km long and longer than the crucible. And in that 15 km it has to also go ftl speeds and support 100,000 crew and colonists without any repairs for that 600 years. the crucible is practically a galaxy wide WMD,so there is the case that the Nexus is far more complicated than the crucible. But in the case of the crucible Admiral  Hacket said the crucible is the largest project the alliance has ever under taken, so the Andromeda initiative would have a struggle building something even bigger and could be said more complicated.                                                                                                                                                                            
However one could say that if a group like Cerberus could do alot by being funded private benefactors, . Cerberus was able to build numerous large stations and a sizable fleet. The issue is this logic is that Cerberus is more than likely larger as an orginzation and has more resources than the initiative does and has been around for about twice as long. We have no idea how long it took them to build anything worth comparing to. Even still Cerberus is considerably smaller than the alliance so they would not be able to build something like the arks or nexus at the same rate at the Alliance could

In conclusion there is no way the initiative could have built 4 arks and the nexus all in 10 years just by private benefactors alone. They most have gotten help for another larger force and i would not be surprised if the alliance is somehow secretly involved with the Andromeda initiative. But what do yall think?