I agree with everyone above about setback removal being pretty beneficial, and working for the story, and that setbacks should be present pretty regularly.
But just from a mechanical perspective, even if you consider adding a boost to be flatly better than removing a setback, it's important to consider where those things apply, and what the practical impact is. Here's my read:
- Boost addition is typically far more limited. Speaks Binary, for example, is not going to start any "That's so borken!" arguments around the table.
- Setback removal is typically pretty broad
- Boost addition seems common for support talents covering things like leadership actions
- Boost addition also seems common in places where difficulty is the primary issue, mainly because it comes from opposed checks. e.g. Stalker.