I'll say that's inaccurate.

The dimensions of all the documents I've written over the years depend on the document class I use, and as our company keeps changing document layout standards every few years, the document class changes as well.. but the only source editing necessary is to replace the very first line in the document, i.e. changing the document class. And the whole document changes. Sometimes completely, much more than just sizes.

Oh, you mean that a PDF cannot be resized? Because the LaTeX document itself is very simple to "resize", by changing paper type, font size, num columns, etc, and you don't have to compile to PDF, you can compile to EPUB or HTML, if you prefer that over PDF.

But, yes, PDFs are intrinsically non-resizable.