-Is there a possibility that spectators of a sport like you and i with no professional training can develop a better understanding of a sport than some professional coaches of some teams?
It is my experience that most athletic, fitness and sports coaches are not good at what they do.
They're usually people who might know some of the basics and have some background in the sport they coach. For them coaching is a 9 to 5 job where they do nothing to expand, update or improve their knowledge base. They continue to use the same basic knowledge they were taught which will often be outdated or obsolete.
As a result, there are fans who are more credible and informed than coaches. Simply due to fans being bigger students of the game and being more up to date. This is a very common theme. Even at the highest levels of coaching in sports, there is a significant proportion of the population that does not belong there and does not legitimately deserve their position.
I think the main accent here from the OP is on football/basketball matches and on similar sports. But what you say about athletic and fitness coaches is definitely true and I can confirm that from my experience. In the area where I live, fitness coaches always stick with the same routine: Traditionally 12 rep 4 set on almost every exercise, traditionally the same low calorie/low fat diet and traditionally the same routine even on anabolics. This industry is most likely bro science in a lot of areas. I have been in touch with a lot of fitness instructors in my country and I haven't seen anyone trying something innovative, like keto diet, 5x5 set/rep, HIIT cardio, etc. It's really boring when you only copy/paste everything and the routine is similar of a robot.