It's not overrated but some rely too much on a test kit to dictate a water change and I'll go as far as saying some obsess with testing water parameters. You're on the right track as far as water changes, nothing can replace the benefits of a pwc
, More importantly during cycling.
I, like you don't rely or use any test kits other than ammonia occasionally and only when I start a new tank. My fish usually die only of old age and once I had a very long power outage I lost a couple.
I understand the importance of cycling and what a tank goes through during that time, but again water changes are the key to a successful tank and especially during a cycle, I always did a fish in cycle with lots of water changes.