When designing a character, you design not only their pros, but also their weaknesses. For example, Olimar in Brawl and Mac in 4 both excel at comboing, but are weak in the fields of recovery and air game respectively. Captain Falcon excels not just onstage, but also kills really well off-stage, but is weak to projectiles. Without any weaknesses, we get characters like pre-nerf ROB and Lucario.
In addition, Marth and Ike have many more problems with approaching through projectiles than Captain Falcon does, since Falcon has his speed and variety while the other two are forced to rely on much more predictable approaches. Run around a bunch and predict your foe's projectiles to see how you can get in and beat them up with your powerful combos!
It also helps if you play on stages outside of Final Destination, which gives zoners an even bigger edge due to a lack of platforms. Battlefield and Warioware are two notable stages that make it hard for zoners, the latter also being ROB's worst stage.
In addition, Marth and Ike have many more problems with approaching through projectiles than Captain Falcon does, since Falcon has his speed and variety while the other two are forced to rely on much more predictable approaches. Run around a bunch and predict your foe's projectiles to see how you can get in and beat them up with your powerful combos!
It also helps if you play on stages outside of Final Destination, which gives zoners an even bigger edge due to a lack of platforms. Battlefield and Warioware are two notable stages that make it hard for zoners, the latter also being ROB's worst stage.