The apparent intention in the unit design interface is that there is no way to build an upgraded (faster-moving or better defended) pioneer like you could in WOM. I infer this from the lack of a "pioneer pack" equivalent.

But you can still build improved pioneers by choosing to "edit' the design. This is apparent bug #1. For example, with the requisite techs and resources you can make your Pioneers have horses or wargs, the Scout talent, and add the other negative talent to reduce the production time a little.

In the game where you create this unit design, these pioneers are fully functional. I've built both outposts and cities with them.

But interestingly, if I use the saved design in a second game, they don't work right (bug #2). They don't get the "settle" or "outpost" options. Instead, they get an option that reads "build road" but that doesn't actually do anything - doesn't build a road, doesn't use movement points.