What do you feel is lacking from settlement building & how can it be fixed?

I've heard people say that settlement-building in FO4 was sort of slapped on late in the dev process. I've heard people say that it's kind of janky. I know I have Feelings (TM) about it, but what are yours? Specifically:

What do you think is missing from or broken with respect to settlement building, and what can be or has been done to fix it (like, are there mods you can recommend that address the issue)?