Hi there!
The default settings try to be the best, or at least the ones more compatible with most websites.
Unfortunately, because of the almost infinite combination of themes and plugins, as well as good and bad coding by developers and site owners, there is no “one setting fits all” for all sites.
FVM has many options to help developers and advanced users to configure several things, so you can either play around with all the settings yourself (make sure your site works properly after each setting, since some of these may not be supported by your setup) or hire a developer to configure it for you and do additional changes that may be needed on your theme to score your scores even further.
For example, you most probably will need image optimization and other stuff on top of FVM.