Even if it’s true it’s not a good argument. You deserve to be paid market rate and if other people in the department are willing to settle for less, that’s their problem.
Just tell your manager you need a moment and want to go see how much your coworkers make. Then go to your co-workers tell them how much you make and that you want a raise and ask them how much they make.
I generally tell people at jobs how much I got hired for within 2 days of joining a company.... there are no down sides.
There are plenty of downsides if your pay is higher than someone with seniority because they aren't gonna like the “new guy” being paid more. Then that will cause animosity between them and their boss for bringing in outside talent instead of feeding the mouths he already has. Then your boss will be annoyed with you for already creating a headache in your first week
And yet every manager I have ever had asks me not to discuss salary with other co-workers to prevent them from getting jealous. Usually in the same discussion where they tell me I am the highest paid one.
This is usually a few weeks before I have an offer for 40% more.
I think they lie because they know they are going to lose me anyways so it's a gambit with a low probability of success, but no additional penalty for failure.