If this has been your experience then you have not seen enough great photo's. The debate between with is sharper, a zoom or prime, has been going on for a long time. Nikon's first mass produced consumer zoom lens, the 43-86? was a dog. But todays zooms hold their own very well, for instance, I own and use three zooms for Florida Wildlife photography, the Nikon 200-400 f4, and the Sony 200-600 are both exceptionally sharp zoom lenses. I also own the Sony and Nikon 600 f4 prime lenses.
To be honest, I do not see much if any difference in sharpness between the Sony 200-600 and the Sony 600 prime.
If used properly by a competent photographer, zoom lenses produce excellent results. I have won several best in shows using zoom lenses.
The argument can be summed up this way, it's the photographer that makes the difference, not exactly the lens. IMHO, both my zoom and prime have produced excellent results.
To pigeon hole or delegate zoom lenses to a lesser status than primes today is just not taking into account the excellent results obtained by zooms.
Below is an old shot of mine using my Nikon D4s and a Nikon 200-400 f4 lens. It has won local and state competitions and remains one of my older stock images that sells well over the years.