No, it's not. You don't leave a big law firm unless you don't want to ever go back to a big law firm just to get a market experience. No. And no, you only leave firms if you need to improve your career.
How do you improve your career? You move to a bigger firm, if you're in a smaller firm. You move to a smaller firm, where you can develop clients. You move to a firm where there's more people like you and you're gonna be happier. You move to a firm that's going to move you upwards as opposed to not sideways.