Are some water valves poor quality?
I think the answer to your question is "all of the above". Yes some valves are made better than others.  Some types (ball versus globe valve) are better than others.  The installation process might have affected them as could how frequently they are used.  Certain elements in your water might also be a factor.

If you don't want to solder a lot or call a plumber, you could replace these with compression fitting ball valves.  You don't need anything other than two wrenches to install these and a pipe cutter to remove the old valves, and of course some spare time.