I'd just like to point out
that AT&T up until the late '80s used to run a large part of their environment around mainframes, many running UNIX! And you probably ought to look up other non-IBM OS's for 370 architecture systems as well. One of my personal favourites was MTS. I saw a demonstration of access to ARPANET (you know, a forerunner of the Internet) from this OS in the very early '80s. Also, for all it's problems, the influential OS Multics was a mainframe OS, and this set features that would appear in UNIX, VMS and a host of other OS's long forgotten.
I was involved with installing and running a channel-based Ethernet device running TCP/IP on a mainframe linking it to Sun and VAX systems in the later '80s (again, under UNIX).
I think that one needs to separate the hardware from the software, as there is a significant difference.
Mind you, if you look as some of the innovations, such as virtual addressing, virtualised systems, key based page level memory protection, I/O offload, multi-processor systems, distributed processing, hierarchical storage controllers, DMA, memory cache, multi-user and multi-tasking, use of ASCII (one of your benchmarks, ASCII was mandated by US government contracts in 1968, and before this was a COMMUNICATION standard, not a COMPUTING one), microcode, solid-state electronics and a host of more minor things, mainframe was often one of the first systems to implement them (often because the features were so expensive to implement, only mainframe-class machines could benefit).
Whilst many of these were not invented on the 360/370....zSeries systems (now the only real mainframe architecture remaining), they were almost all pioneered on mainframe-class systems like Atlas, KDF/9, Cyber/CDC, UNIVAC and others.