It all works in conjunction.
For example, a scout watches a player several times over the course of a few months, puts together a profile of strength and weakness, etc.
But that might not catch on to a subtle trend over the course of the season. Perhaps the numbers show that player consistently spends a lot of time in their zone, which didn't happen to be initially apparent to the scout, or the player sucks at "insert whatever fancy stat". The scout can then take that information and watch the player more with an emphasis on contextualizing that part of their game, which can help inform you on whether it's something that could be improved on over time, is a problematic hole in their game, or is maybe just a situational thing.
It's not a eye test vs. numbers thing. They work together.