Your point is right as long as there are frequent trains introduced from CCT. But the point is when the same is not happening.
For a simple ex: consider connectivity to BZA and VSKP from CCT.
For the past decade and a half, the best and quickest option to reach BZA or VSKP for people of CCT or to reach CCT from BZA and VSKp is always Ratnachal and Janmabhumi. Infact, other than BZA and VSKP, both Ratnachal and Janmabhumi have the maximum influx and outflux of passengers in RJY...
more... and SLO.
Both the present passengers to VSKp and BZA originating are at @ 4 30 am and 4 45 am.
If there is another ICE, originating from CCT towards BZA ad VSKP, then people would be opting for that. But the point is there is no such making people move to SLO
At the same time, CCT cannot keep on asking for trains originating form it for its passengers, at one point of time it gets saturated. Saturation levels are already nearing now.
On a bottom line, the demand of main line connectivity can be met to an extent if infra is developed at CCT and trains are introduced on a frequent basis.