I don't know where you got the figure 25 %. Normally, anything under 10% is good. Defragmentation is a controversial topic. There are many different views from very many people who are quite educated in computer technology. The Web is full of information about this. A person can use search engines and find enough information to keep them busy for a long, long time.
If the information I have added to this forum helps anyone, then that is good. On the other hand, if the information I have added is not useful, then it can be ignored.
You have a great day.
"PEOPLE ARE MORE IMPORTANT THAN THINGS"