In Modo a simple Join Edge command exists to take care of this situation in one step:
Obviously I can merge the two vertex pairs, but this is a rather long-winded way.
Is anyone aware of a simple 1-step method? Or and add-on with a similar command?
There is an addon for this simple cases . âEdit Mesh Toolsâ comes with blender , under utility tools âmerge by distanceâ.
Unfortunately, that doesnât work at all for me. I did try that option a few days ago, and it just collapses edges uncontrollably because the distances between edges are too irregular.
Besides, even if it would work the edge would not be centered.
Weird that Blender doesnât have a simple join edge command.
Unfortunately that is not true.
Ctrl-E > Bridge Edge Loops > Enable merge in the tools options pop up. It should remember the last checked option with the consequent uses.
You meant âfortunatelyâ, right? 
Thatâs exactly what I was looking for. I did try the Bridge Edge Loops option before, but missed that Merge option! Works as advertised.
Many thanks @kkar !
You know what I meant!
Just pick my answer as the solution so others who search for can get to the bottom of the issue asap.