When I started Publisheet, the idea was that it would allow users to create static, web-based reports from their spreadsheets, including textual information that would be written as Markdown (with a WYSIWYG editor) directly in one or more cells. I thought that it would be an easy way to create complete financial reports, for instance. The landing page's images still reflect that.
But as soon as it launched, I noticed that no one was using it for text-heavy reports. People just wanted to publish their spreadsheets online, as is, with formula support. So, I started focusing on that and ended up in this crowded space, as you correctly state.
I think that Publisheet's main selling point is that it's really simple to install and use. There's no .exe to install, there is no need to upload the Excel file in the browser, there is no form builder. Also, it works on Windows, Mac and in Excel Online. You basically click Publish and it's done. But I am aware that all the systems you listed are way more feature-complete than Publisheet and it is something we'll have to improve.
By the way, congrats on Calcapp, it looks really polished!