Although, what about the Stellar Folding technology the Terrans could research in TotA? Wouldn't it be sophisticated enough to travel between galaxies? Most importantly because it outright stated that "With infinite energy, one could use Stellar Folding to travel to any point in the galaxy instantaneously."
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In theory, maybe, but isn't it a moot point until someone has infinite energy?
Also, what engine-technology did the Precursor use? It had to be better than Hyperdrive, because, as Tandis explained in the last mission of the TotA-campaign, the Precursor wanted to "deal" with the Andromeda-galaxy in order to prevent it from colliding with ours.
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While it's likely that the Arnorian FTL drive was something more advanced then hyperdrive, I think it's possible that they used an entirely different method than normal for intergalactic travel anyway (stable wormholes, maybe?).