Fields can do two things really, really well. First, he can run. He's always a threat to take off and defenses have to account for that. Second, he can throw a deep ball. He was the most accurate passer in the NFL last year on balls between 31-40 yards and the 4th most accurate on 41+. Where he struggles is on is short to intermediate passing plays. Quickly making reads, going through progressions, and fitting the ball in tight windows is where he struggles.
Fortunately, what he does well are the biggest needs for a QB in Arthur Smith's offense. Smith likes having a QB that's mobile. His offense is run heavy and having a dual threat QB gives him more options in the run game. Smith also likes to rely on play action to keep defenses honest. Again, that's a strength of Fields.
Fields will probably never develop into a complete QB at this point. But he's way better than Ridder and actually brings a couple tools that play well in Smith's offense. I'd prefer the Falcons fire Smith and get a competent head coach but if we're stuck with him, it would at least be more fun to watch Fields.