Correct. You can also periodically douse the cracks with boiling water, but nothing will totally prevent weed growth. Weeds are just the name we give to pioneer and other exceptionally hardy plant species that evolved to take advantage of precisely these sorts of inhospitable conditions.
I have nothing against the use of glyphosate in general but I would try to avoid frequently spraying any herbicide or pesticide, including Roundup, on surfaces where people and/or pets are often going to be hanging out, consuming food, etc.
The OP’s best strategy IMHO is to set out patio chairs that are low enough that the people sitting in them can just tweak out little sproutlings from the cracks and throw them into the firepit. You’d be surprised at how easy it is to keep a small paved area weed-free if you just get into the habit of plucking out the inevitable few bits of new growth at regular intervals.