There needs to be a differential analysis of what metadata or relationships do not exist in which formats.
Just some resources looking at "core elements".
The following in an interesting expose into the use of "kits" or records for more than one carrier type. Arguably this is 90% of linguistics.
https://original.rdatoolkit.org/document.php?id=lcpschp3
https://original.rdatoolkit.org/document.php?id=lcpschp7
https://www.loc.gov/aba/rda/pdf/core_elements.pdf
https://www.follettcommunity.com/s/article/ms-marc-rda-core-elements
https://www.librarianshipstudies.com/2016/03/rda-core-elements.html#:~:text=Core%20elements%20in%20Resource%20Description,Types%20RDA%20Core%20Elements
https://wiki.gccollab.ca/PFAN_-_Core_RDA_Elements_for_PFAN
https://cornerstone.lib.mnsu.edu/cgi/viewcontent.cgi?article=1017&context=olac-publications
Conser is for serials
https://www.loc.gov/aba/pcc/conser/index.html
Bibco is for other bibliogrpahic records.
https://www.loc.gov/aba/pcc/bibco/index.html
Maps and cartograpihc information