You might want to be more specific by what you mean by "modern", because there were certainly machines with demand-paged virtual memory before the VAX. It was introduced on the Manchester Atlas in 1962; manufacturers that shipped the feature included IBM (on the 360/67 and all but the earliest machines in the 370 line), Honeywell (6180), and, well... DEC (later PDP-10 models, preceding the VAX).

My impression of the VAX is, regardless of whether it was absolutely first at anything, it was early to have 32-bit addresses, 32-bit registers and virtual memory as we know it. You could say machines like 68k, the 80386, SPARC, ARM and such all derived from it.

There were just a lot of them. My high school had a VAX-11/730 which was a small machine you don't hear much about today. It replaced the PDP-8 that my high school had when I was in elementary school and visiting to use that machine. Using the VAX was a lot like using a Unix machine although the OS was VMS.

In southern NH in the late 1970s through mid 1980s I saw tons of DEC minicomputers, not least because Digital was based in Massachusetts next door and was selling lots to the education market. I probably saw 10 DECs for every IBM, Prime or other mini or micro.

Period might be the best word. Contemporary is also a contender I thought of first, before disqualifying it for implying 'modern'.

Also Prime as well in the 70s pre-VAX.