I have zero experience, as I stated in other thread, in making debs - but I feel this can't be correct...
...because you don't specify the /opt/ destination at any point. I mean, packages can install things to many different directories, there's nothing magic about /opt/ that makes it the default if not specified.
You
might have misunderstood the --dest flag, or
perhaps something is missing from the command.
Have to tried this to see what's reported?