One improvement in Picard 2.0 is that it uses the JSON version of the webservice (although it is a pain changing a plugin to work with JSON rather than XmlNode). As well as being a more logical format, it does return slightly more data (see Difficulties with work artist aliases). Now it will return aliases for recording.relations.work.relations.artist - at least when artist is “type: composer”.
However, if the type is “type: arranger” it seems to return an empty list of aliases, even if they exist in the MB database - see track 6 of this: https://musicbrainz.org/ws/2/release/e6bf7d96-2628-3db5-add5-287f4cd2c1ea?inc=release-groups+media+recordings+artist-credits+artists+aliases+labels+isrcs+collections+artist-rels+release-rels+url-rels+recording-rels+work-rels+recording-level-rels+work-level-rels&fmt=json
Levon Atovmian has aliases but they are not listed in the JSON
On the other hand, this one - https://musicbrainz.org/ws/2/release/0aadac63-79e4-4374-8757-a36f887a8121?inc=artists+artist-credits+artist-rels+recordings+recording-level-rels+work-rels+work-level-rels+release-groups+labels+aliases&fmt=json does have aliases for Rimsky-Korsakov as orchestrator on track 4.
Any ideas why this should be?
EDIT: It seems fairly random, since in track 4 of the last release mentioned above, Glazunov is also listed as an orchestrator, with an empty alias list although he has aliases in the MB database.