Are there cases where dentures are better than full-mouth implants?

Yes, there are such cases. A denture can be the more sensible choice when 1) the jawbone has resorbed so much that placing multiple implants is difficult, 2) uncontrolled diabetes, cardiovascular disease, or similar conditions make repeated surgeries risky, 3) advanced age makes a long treatment course hard to tolerate, or 4) you want to keep costs down. There is also the option of starting with a regular denture and later switching to an implant-supported denture (overdenture) by adding 2-4 implants to improve retention. After a thorough diagnosis, we can discuss this together.