Directionally, I agree with this, but it's important to be clear that it varies by jurisdiction. A blower door score of 3.0 ACH50 (air changes per hour at 50 pascals) is code in some states, while a less-performant 5.0 ACH50 is code in others. Neither of these are terribly "air tight" and you can generally get to 1.5 or even 1.0 without too much additional effort.

But my 1920s house – built very sturdily – scored a 19.5 ACH50 when we moved in, and after a not-insignificant amount of weekend work is now at a 10.33, well off from modern code even in lax areas.