The slow start behavior you describe is not inherent to TCP proper, but rather, a detail of the congestion control algorithm in use by the endpoints' TCP stacks

The slow start behavior you describe is not inherent to TCP proper, but rather, a detail of the congestion control algorithm in use by the endpoints' TCP stacks. Most such algorithms will have some kind of AIMD feedback loop to achieve some balance of fairness and efficiency. But for applications where you have control over the endpoints and the network in between them, you can minimize slow start by setting a high initcwnd/initrwnd and using a less aggressive window shrinking mechanism.