It's not clear from your post what your role really is (is it something like lead dev? or just a more opinionated member of the team?) but if you're not managin

It's not clear from your post what your role really is (is it something like lead dev? or just a more opinionated member of the team?) but if you're not managing the team directly, then don't manage them. It's not your job and no-one likes that. If they wanted to make you the manager, they would have. And they didn't. There's really only way to help improve a codebase / development process in a situation like this: one small incremental step after another, for a very very very long time. If you don't think you can enjoy that and have the patience to stay with the problem for a few years, consider looking for another job.