Garmin Coach can never replace an actual human being who interacts with you, sees you running, sees the little things which make all the difference to your personalised plan such as lifestyle influences.
It also depends heavily on what your targets really are. I don't particularly want to get significantly faster mainly because I already have difficulties seeing where I am going as thing already are. Garmin coach just wouldn't comprehend this and couldn't provide me with guided runs from time to time.
Injuries come from a variety of things including over training, under training, accidents whilst training, not warming up / cooling down properly, badly fitting or inappropriate for other reasons shoes, etc.
My approach is to minimise the risks to me and to increase my distance. I am finding that increased fitness and associated steady weight loss is resulting in my average speed slowly increasing as it is.