And the compressor does not think: "how can I make these two sequences align better without wasting a lot of space?"

No, because alignment, in the general case, is O(n^2). It is ironically one of the more tractable and well solved problems in bioinformatics.

The compressor doesn't think about anything. Also, Zstd doesn't have the goal of reaching the highest possible compression ratio. It's more geared toward lowest overhead, high bandwidth compress/decompress.