I'm in that sort of job, for the same company. Been applying for driver roles for just as long. Depending on your age and experience I think the job earns pretty well, when compared to other "customer service" jobs. For one you are paid a salary, not an hourly wage. The job will also pay off in terms of the situational answers you would give in an application to be a trainee driver, and the answers you would give in an interview.
It's not a free ticket to becoming a driver, but the experience gained from any railway role would be beneficial toward your application, especially if you are proactive in your role. For example, for trainee driver, you would probably be asked about a time you dealt with an emergency situation. There will be plenty of relevant examples experienced in a customer service role for sure! Just hang in there though, the process into getting a trainee driver role is very long.