Maybe Hasek intended a double meaning of "dobry vojak" as a) good-natured soldier and b) high-quality soldier (which would be sarcasm), but TBH the option b) just never occurred to me (I'm a native Czech speaker).
"Good" ended up the default meaning in many Slavic languages, but its original meaning was much broader (https://en.wiktionary.org/wiki/Reconstruction:Proto-Slavic/d...), and AFAIK those other meanings are still understood if considered archaic - is that not the case in Czech?
Is it really that broad? There are many examples, but none really deviates from "good". In pretty much everyone of them, I could just use "good" and it would work OK.
The only reference to "dobry" meaning "brave" is this:
> Cognate with Latvian dabravecis (“brave, prudent man”).
But Czech was likely not heavily influenced by Latvian.
Honestly, I think people should just stop assuming that if word X means Y in a Slavic language A, that it should have the same meaning in a Slavic language B. I see these kind of broken assumptions very often, but there are way too many false friends for this to work.
Czech "dobrého vojáka" is more "of brave (in `dashing` conotation) soldier".
So Hašek's humor starts right from the title.