Old VMS programmer here. In addition to the above, the thing I remember is that there was more of everything in VMS, and it was all more complicated.
Unix has files which are just strings of bytes. VMS had those, but also several (or many) other file types with records and indices kind of like a database, and a library of functions for each different file type.
Unix has processes. VMS had processes and jobs -- a job is a group of processes, when you log in you start a job, all the subprocesses you start in that login session belong to that job etc. So there are functions for dealing the jobs as well as processes.
Unix has environment variables. VMS had logical names which could be used in a similar way, but there was a process logical name table, a job logical name table, and a system logical name table, and functions for dealing with all of them.
And on and on in this style. Whether you see this as an advantage or disadvantage depends on whether you have an application that can use some of these features, so you don't have to write them yourself as you might have to in Unix.
In addition to that, as the link above explains, VMS had facilities that early Unixes just didn't have, such as clustering - you could connect several VAXes to a common shared file system and share computational load. Also there was DECNET, a complete networking stack, a parallel universe to TCP/IP (which was not so pervasive in the 1970s and 80s). Each of these contributed a couple of thick binders to that wall of documentation.
The VMS manual set was delivered on a pallet! It was bigger and heavier than most of the later VAX computers.