You do have a strong competitor in this space. Adobe. Which is admittedly costly for the the pro version, but can't be ignored. Why use PDF otter over them?
For filling in individual PDFs, yes, Adobe wins. However, I'm using the editor on my site to show off the PDF Otter API which helps you fill-in PDFs at scale. That's a tool that Adobe doesn't provide and how PDF Otter will earn money. I'm sorry that it's poorly advertised. I'm working on improving the homepage's copy and making it easier to transition from the demo to using the API.