Ant-Man was able to handle the Quantum Realm on his own in the original, but it’s possible that he needs Doctor Strange’s help in Ant-Man & The Wasp.
The now-obvious connections between Doctor Strange and Ant-Man only continue to deepen the bonds between characters within the MCU as it evolves toward the end of Phase 3.
Paul Rudd enters the Quantum Realm in the original Ant-Man and can barely escape the dangerous subatomic dimension.
There’s still a chance that Marvel is risking over-saturation of the Doctor Strange character by having him appear in so many different upcoming MCU films.