The concept is really simple. You can either build to be really really really good at one thing(specializing) or kind of good at a lot of things(generalizing).
If you only face the thing you are really really goot against then specializing will be really succesful.
If you need to compete in a lot of different situations then the generalizing will be more succesful.
As a player you can use your mobility to focus the kinds of encounters you are in to match up with your build (specialization/generalization). This is what we called skill.
neither specialization or generalization is inherently better then the other its based more on what the landscape of encounters looks like at any given time.
And even in the specialization route it generally takes more then just a single command. That sword spec needs to get enough dam roll to make that flurry scary, they need to perfect some very time consuming skills, and they need to be able to handle disarming/maledictions as well or they can't use their cannon.