How to tell it’s time to find a new coach
The short answer: His/her video collection is on VHS.
The longer answer: A lot has changed since the 1980s. High-speed video has given us insight into things we couldn’t see before. But some people still cling to the “old ways,” like the Pagans in medieval times.
Their rationale is that they’ve been doing it that way for X number of years and have had success. Yet it’s likely they had success in spite of what they teach instead of because of it.
There is plenty of good information out there. And tons of video of top-level players out there. The simple test — aka the Hanson Principle — is compare what people tell you to the best players in the sport. If what you’re being told doesn’t match what you see, it’s time to find a new coach. There’s simply no excuse for accepting bad teaching.