Hi there!
I do own a physical copy of
Planet Unknown (and am eagerly awaiting the arrival of the
Supermoon expansion), so I can answer your question:
The game comes with only one copy of each asymmetric planet and corporation, as you surmised.
This could be easily overcome in an electronic version. Alternatively, as you also mentioned, it may be the game designer's preference that players do NOT do this.
I would be okay with allowing multiple electronic copies of the same corporation. However, my original suggestion was even simpler:
All I proposed is a house rule to remove the Makeshift corporation from the options for arena games.
Although corporation choice is random, the overall impact does not even out. The effect on an individual game is obvious to all, I think. Now consider the case where there are three players and only three corporations, distributed randomly each game. Assuming a basic level of familiarity with the game, the player who receives Makeshift will win each game, even if the three competitors have rather different levels of expertise. Over many games, this random distribution leads to each player winning one-third of the games -- entirely masking the difference in skill levels.
This is an illustrative example. The actual impact on the arena is less than this, as Makeshift is one of eight corporations, so it will appear in about 40% of the three-player arena games (rather than the 100% appearance probability in the example above). But the point still stands. When it does appear, the outcome of the game is basically known, because Makeshift is unbeatable.
I will finish by repeating my proposal: For arena play, we should remove Makeshift from the available corporations.