lmms does not require or at least works perfectly reasonably without at least the following packages and/or USE-Flag requirements, which it currently depends upon:
Besides, the dependency on LADSPA
could be subjected to USE-Flags (ladspa) and is questionable in that generality as a whole, as the above.
Given that it works without /any/ of the packages listed above and I do not see them bundled, I assume the depdencies are bloated.
Recently there was a new LMMS 1.0 released. All these have been moved into the ebuild as RDEPENDS, and they are being evaluated to see if they are still necessary.
I've tried to take good care to not add useless dependencies in recent lmms versions.