> If it was flat but exponentially grew after you went on a hire spree, you know where to look at.

Initially, one could churn out a lots of features quickly accumulating the technical debt. The increasing time can be rather more about the past, then new people you hired.

> If it was flat but exponentially grew after you went on a hire spree, you know where to look at.

It takes time for new hires to get familiar with the code and for seniors to help them get up to speed, so I'd be surprised if a hiring spree didn't end up sharply rising curve for feature rollout time.

This assumes all features have equal complexity.

This assumes a lot of other factors, but I'd say they all converge.

You won't have high code quality without a motivated and competent team for instance. Same if they can't correctly scope their features or engage in long unplannable projects, etc.

I'd make a parallel with clean natural water: you can't have it in isolation, the rest of your environment needs to be functional to preserve it.