Thanks for sharing this and other post mortem's, and for pointing out the backtrace delay before:
How to opt-out of swift 5.9 “interactive exit” behavior? - #14 by taylorswift
There they mention the SWIFT_BACKTRACE environment variable, which supports disable:
swift/docs/Backtracing.rst at main · swiftlang/swift · GitHub
Did that not work to avoid confusing systemd?
It seems doable to set that before running a script (and to have different settings depending on what you are launching).
The uncontrolled crash default seems like the safest thing for first-failure data capture, since the developer could have caught the error, and since it can be disabled by the deployer. Frustrating, though!