You need to think holistically. Subsonic Babur can easily be shot down once detected by SU-30 stationed in Punjab sector or SU-30 stationed In Rajasthan Sector. From there SU-30 or any other fighter can shoot down the Babur1B.
So Babur has to take a long way to reach, Lets say Punjab sector. It will not fly in straight line to avoid Early detection at all. So In order to evade and reach a Highly defended area, Babur definitely would need longer legs (Long distance). A 1000-1500 KM babur is better in evading and striking a S-400 battery situated 400 KM from Lahore than a 600-700 KM babur which will have limited legs or waypoints configured to avoid detection
Most of the Babur in Rajhstan sector will be striking India through sea. They will fly From Sea, hit targets in Gujrat and nearby localities. So How a 450-700 KM Babur can make long evasive moves when striking a target at 500 KM?
Hence range factor comes in. Longer the range, longer Cruise missile can loiter and go over the area and wait for new commands to strike a new target. You will have the flexibility that limited range Babur now wont be able to provide