I too have well over 10 years experience on mainframe, mainly cobol and db2 on z/os. limitations could be put in place for numerous reasons, including, inter alia, the transport mechanism used to move the files (e.g. x'com), network restrictions and, as stated, user (lack of) knowledge.
however, the mention of "jcl limitations" is just incidental to the actual question, i.e. the most effective and efficient way to import the data and populate an SSAS cube.
Space, the final frontier? not any more...
All limits henceforth are self-imposed.
“libera tute vulgaris ex”