Solved!

Instead of using testRunner.runTestStepByName("SUBMIT_WS_REQUEST") in the called script, I also added a full path call there as well like so, and it works!

def testStep2 = testRunner.testCase.testSuite.project.getTestSuiteByName("MIR_TESTS").getTestCaseByName("DEVICE_LAUNCHER").getTestStepByName("SUBMIT_WS_REQUEST")

testStep2.run(testRunner, context)