A lot of classical music is this way to be honest, there is a lot of formulaic composition (I don’t mean that derogatory at all) and once you get the patterns it’s easy to extend, maybe even play it like a fake book.
I recall a lot of what we know was originally something closer to figured bass in the first place and later fully arranged by someone who wasn’t the original composer. Or, take a look at Mozart Requiem for example, only a small percent of which was actually manuscribed by the man himself.
One thing that frustrates me about music notation is that when you have a key signature with lots of flats or sharps, it's hard for me to tell at a glance what the accidental is doing relative to the key signature. I've gotta look back and remember what was the unmodified note.
5 flats is easier to play mechanically, imo, because hitting black keys is often easier