Hi Timothy, thanks for reporting. The whole file organization of syslinux (both which file is in which package, as well as the location of files) needs improvement. This is something I intend to work on during the bullseye cycle.
As part of that, I'll also look into whether we need both the perl script and the binary of "isohybrid" and in which package they should be placed. It'll still be a while until I get to it though (most likely towards the end of this year). @Thomas: If I remember correctly, isohybrid.pl only needs perl-base (which is an essential package and does not require a dependency). I'll double check that too. Regards Lukas