More or less, today's lenses are better than yesterdays. Historically, yes, primes have been substantially better than zoom lenses. Most modern primes are still outstanding. Zoom lenses, however, have steadily improved -- better coatings, lens formulas, and more precise glass grinding has allowed zooms to improve substantially. Pro level f2.8 zooms are typically the best and often rival prime quality. Lower end zooms are often still great, though a clear step below in all but the best circumstances.

One piece on zoom range worth mentioning: in general, a smaller zoom range results in a higher quality lens. Your 18-55 is a 3x zoom, and the 55-200 is about 3.6x. The 18-200 is about 11x and the 18-300 is 16.5x. Those are big jumps and fitting such a wide range does require some compromise. All lens choices are a matter of compromise -- size, weight, optical quality, and cost are all determining factors, after all.

It's true, you won't find many modern primes in the 135-200 mm range. In that range, I think you'll find most people recommend a 70-200 mm f2.8 zoom -- yes, it's so good that the primes in that range have fallen out of favor. However, I have a suggestion: remember that your D3100 is a crop sensor body; Nikon's 85 mm 1.8 becomes about 130 mm on your D3100, right around the focal length you prefer.