Verdict: hledger has its quirks and issues, and I had to write my own MT940 importer, but it is orders of magnitude nicer to work with than the horror that is GnuCash
Like, I basically started over my bookkeeping for the entirety of 2022 and 2023 (so far), from scratch, with hledger, and it *still* took me less time and frustration than it likely would have taken to finish the last bits in GnuCash