There's an easy answer to this question: it would double the benefit to all other options.
There are NO settlers in the game, just pioneers. When you build a pioneer (assuming you also start with pioneering), it costs a ton of resources. More importantly though, when you use a pioneer to build an outpost, it *also* comes with its own soldier. So with a pioneer, you get a new outpost+soldier. That would make it far more overpowered compared to the rest of the starting perks.