I am a huge proponent of the fourth core is the setting.
The reason is, 2024 is careful to avoid a "default setting". There is a default, in the sense that the same information in the 2014 core books is also in 2024 but it organizes differently. 2024 is easy to modify and replace.
From a worldbuilding perspective, 2024 is the best edition of D&D so far. It has lots of tools, tons of information ready for use, and all easily manageable.
This is why choosing a specific setting is necessary. Maybe via old school (and DMs Guide Greyhawk setting), one can use local adventures somewhat randomly, and see what setting emerges and evolves as a result. Even then, a DM needs to make some decisions about the world setting, for characters to get a sense of place in the world.
Because the 2024 leans setting neutral, one might expect the Monster Manual to lack flavor. But actually there is lots of tasty flavor. The monsters tend to lack "history", which they gain as part of a detailed setting. But the monsters do have "concept". The flavor is in their concept. For example, the Goblin is a Fey creature. The Goblin has a distinctive context and meaning as part of the multiversal setting. The Feywild is flavorful in concept. What the Goblin is, a Small creature that is obsessively excited or incompetently malevolent now situates within the magic and whimsy of the Feywild. The Goblin is a fun concept. Of course, this is how reallife fairy tales often portray "goblins". But 2024 can do this concept well. The Goblin has a remarkable amount of flavor even before the creature steps into the history of any particular world setting.
Analogously, many monsters of the Monster Manual heighten the flavor of the concept.