@Eli6 Sorry for the late reply.
You can easily find out the total #lines of code, e.g. using the tool cloc.
It return for restic:
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Go 388 10383 4453 49061
and for rustic:
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Rust 44 873 279 5497
However, a fair comparison is very hard. First, the functionality of rustic and restic differs (rustic currently misses more functionality than it adds). Second, restic has many tests included whereas tests coverage is currently really poor in rustic. And third, it of course depends a lot on what functionality is provided by other packages/crates.
But feel free to have a look at the code and make a judgement yourself!