Earlier quoted context omitted.
I'm a fan as well. My org ended up dropping our draw.io intergration in Confluence in favour of Lucidchart; I'm still not really sure why as it appears to be worse in functionality as well as slower and more tied to a cloud backend.
In what ways is Lucidchart worse in functionality? (disclaimer: employee of Lucid Software)
Last time I used it, before switching to draw.io, it became slow to the point of being unusable once you had a few pages in a document. And I was making an animation where each page showed the next step in a process, so there were a lot of pages.
This was a couple of years ago, so things may have changed since.
My diagrams may have a bunch of elements on them, but I don't think I use any advanced features (irrespective of whether it's Visio, LucidChart or draw.io). From that perspective, these isn't much difference between any of these programs, so there's just no reason to use a paid product.