The other side of the coin is that some designs of the past are superb and have scarcely been surpassed. In fact in some cases, other than in the area of multi-coating technology, some designs from the 20's and 30's are every bit as good as those from today's supercomputers. There are no simple answers . Some Sigmas and Tamrons are good, others aren't. Nikon has some lenses which are better than Canon's, and visa-versa.
Primes are great for fast apertures, zooms have greater versatility.
Usually price is a good determinate of quality you generally get what you pay for. Enjoy and stop fretting.