I've seen so many developers over the years who view having to rewrite that module because it can't scale well enough anymore as a failure, but I call it a success. Software is meant to be tumultuous, things SHOULD be getting replaced.
In another post in this thread I mentioned that software systems are like children in that they have phases. Assuming that your company and software team is dedicated to fixing those issues (slowly, beside new features), then I think you're probably in a healthy spot despite the pain.
An observation is that business interests must ALWAYS trump technical interests when those business interests are critical. No business = no technical. But at some point when the company becomes stable that balance has to start shifting back towards the technical or the company itself becomes ridiculously inefficient.