This is the correct reason. Ultimately Soviet Union lacked the financial resources to compete at this scale. All of the other problems that are listed as part o

This is the correct reason. Ultimately Soviet Union lacked the financial resources to compete at this scale. All of the other problems that are listed as part of it, the engineering feats that are required, the technological advancements that are required, etc... all come down to money. If the Soviet Union was able to achieve the same or greater spending power that the USA was able to at the time, the competition would have been different. Because all those other problems get solved by throwing enough money at them. The early achievements of the Soviet Union were natural logical progressions from the V2 rocket. It was a small step that replied on the same level of engineering. This is why they were able to achieve first man in space and for satellite and so forth. The scale of the problem to get to the moon and bring someone home is so massively different that it's even difficult for us to replicate currently.