However, the different space agencies and rockets are not as similar as you suggest, especially as the game gets more difficult in the midgame. For example, China has reduced building upkeep and building cost and the difference can be a lot of money. Japan has really powerful contractors that either boost science or save a lot of money on rockets, allowing you to throttle up or down to match your available mission slots. Mars Horizon doesn’t let you fail outright, but especially in the midgame, playing to the agency perks is critical to not stalling out.

The rockets are also not as similar. It’s true that the tech tree is quite similar for all agencies, but looks are deceptive. USSR gets to launch all early game payloads with one set of components, but pays for that convenience when the R7 overperforms for the mission requirements. The agency-specific rockets also have different build times and costs. The most extreme example is China, which can farm manned moon missions easily with their Long March 2F. It doesn’t seem like much on first glance, but the price and time difference between a Saturn, N1, and the Long March 2F makes a huge difference in how much the mission is worth. The Jupiters and Delta IVs, while available to everyone, are actually suboptimal choices, costing more and taking longer to build.