There is a lot to unpack with this question, but…
I’ve never used sitebuilder, but based on the small amount I’ve read about it, Pinegrow is quite a bit different.
Pinegrow helps you to write clean HTML and CSS. It also has tools to help you use a number of popular Frameworks like Bootstrap. You can create ANY static site that is out there. It doesn’t play that well with some of the new frameworks like React. It does play well with PHP. You can integrate with PayPal/Square fairly easily. The forum has a section for people to showcase the sites they have built for examples.
Your pages aren’t going to automatically be fluid - that is something that you have to design and implement. If you use a framework, like Bootstrap, as a starting point, this can be fairly easy. Doing it from scratch requires a little more knowledge.
Pinegrow puts you a lot closer to the HTML and CSS source code than many other page builders, but still offers drag-and-drop simplicity. It is a great tool for getting to know HTML and CSS better, but would probably require a little more understanding of code than sitebuilder or Wix. It will offer you the ability to infinitely modify your content (well, within the bounds of web page programming).
With regards to “publishing” your site. Pinegrow is a tool for building web pages, any hosting or uploading of files to that hosting are done outside of Pinegrow. As a negative, you need to know a little bit about setting up your site, but as a positive, you aren’t locked into Yahoo (which then tanks your builder and ability to make updates) or some other proprietary site that can decided to block content or raise prices without any alternative.
My 2 cents (and BTW, full disclosure, I work for Pinegrow).