muscle imbalances

The balance of strength and mobility across the muscles and joints of your body is what is really required when you think about the importance of posture.
Look, everyone wants to do the fun stuff, but you need to pay attention to the pitfalls of ignoring how your body is supposed to move because it will bite you in the ass.
Your imbalances are setting you up for major consequences, if you don't address them.
Train around your lousy mobility. You don't get to skip strength training just because you're as flexible as a fence post.
Pain doesn't occur in isolation, so injuries should force us to look for breakdowns in our chains of movement as a whole.