Practice alone is useless, akin to running around in circles, endlessly repeating whatever dim knowledge you already posses in hopes of acquiring more.
Practice + study is where the progress is made, the people in DA who never improve are just "practicing", never consuming new knowledge, just going over and over and over again the little they know.
Don't just save tutorials, grab the books, the videos, internalize their information religiously, and practice based on said information, don't ever sit down to scribble hoping for improvement to come magically to you in the form of epiphanies or revelations, look after it yourself.
In short: practice is meant to reinforce what you know, never to improve, studying is what gives you progress.
And no, unless you have a learning impediment or something, everyone can improve, again, the people you've seen in DA are majorly autistic and apart from not studying, they hardly ever draw.