BPMN Parallel Gateways appear to execute sequentially rather than in parallel

Issue

We have a BPMN process that contains a route within which executes 5 REST tasks through parallel gateways.The processing time of the parallel execution and convergence should be at least somewhat similar to the execution time of the longest running REST task. But
unfortunately, execution timing of the parallel routes to appears to be at least the execution time of all of the REST tasks combined.