The method you described is called the "robot" method, where an unattended computer running a continuous timer loop performs a filemaker-pro-only action. You are right in your reasoning for filemaker servers rendering limitation. I like JohnSindelar term for it: "headless".
An advancement to that technique is to use something like the RemoteScripter plugin to perform the robot function on-demand:
The "on-demand" robot technique is also covered with sample code here:
and an explanation on how to do it without plugins in further detail here:
The only other legitimate way I know for creating PDFs is to use a PHP script with a PDF generation package like TCPDF to generate a PDF result via URL, using a static template filled with CWP filemaker data. A lot of work, but fairly reliable. DBServices covered this method on their blog:
All in all, I agree, it sucks that you can't "natively" create a PDF in WebDirect or via Server Scheduled Scripts. But there are ways to do it without waiting for a robot cycle.
There are other legitimate ways to create PDF files which can be done on the server and triggered from Go or Webdirect aswell as Pro or Advanced. And my particular favourite also works from runtimes too.
Using ScriptMaster with the iText library is my favoured flavour (but there are also a couple of other ways too, just not keen on advertising them..)
There is arguably as much to learn as there is with learning PHP (OK maybe a bit more) but significantly more you can do this way that is NOT possible with PHP-type scripting which pretty much focusses on initial creation, not subsequent manipulation.
My experience is not that this is fairly reliable, but that it is completely reliable. Many happy customers and complex solutions attest to that.