In rec tennis such ratings have less to do with tennis skills in the formal sense and more to do with win/loss record.
You can easily rise to 3.5/4.0 and even become a city Champion in a place like Atlanta while having a weak/dink second serve and terrible ground strokes. All you need to do is knock the ball over the net one more time than your "I Wanna Hit Like Nadal" opponent who gifts endless UEs and the match.
Matches between most 3.5s/4.0s who have figured this out go on forever since neither can generate enough pace or is accurate enough to finish points without generating too many UEs. They patiently hit the ball back to their opponent waiting for a UE.
Now, there are some 3.5s/4.0s who might have some pretty strokes, at least once in a while. And if they're really disciplined they might even exploit those nice strokes at the right moment during a match. But most "top" 3.5s/4.0s are simply the most patient players among many, many impatient players.
I know this based on personal experience and observation. We have a ton of 3.5s/4.0s at our club who can't generate pace, at least with consistency or accuracy. And stroke-to-stroke everything is highly variable. But some often win big since they patiently wait for an opponent to self-destruct, especially in singles. I even know some 4.5s with terrible form but they win because they consistently get the ball back no matter how ugly the shot.