At some point, I actually paid for LucidChart for a year.

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.