Feel free to quote me.
For the long time users of Land Desktop and Civil 3d you have relied on a command to Add Vertices to 3d plines. Things have changed and you need to recalibrate your skills. After getting over my initial anger and frustration thinking I’ve lost functionality. I found a blog post by Scott McEachron that brought the “duh” back into my internal conversation.
Insert Elevation Point then use the Increment option.