Instead it was a loose union of principalities, bishoprics and duchies that didn't have any sort of unity among each other.
In 1701 or thereabouts Frederick I was allowed by the Holy Roman Emperor to call himself King IN Prussia (i.e. in the independent duchy, but not in Brandenburg which was still feudally subject to the Emperor). Frederick II the Great in 1772 was powerful enough to declare himself King OF Prussia, having taken over the various other bits of Prussia under direct rule (instead of owning them as a subject of the Emperor).
Shortly after this, the HRE dissolved entirely.
Re: Habsburgs, there was a Habsburg Emperor in the HRE, but the Habsburgs were very extensive and also ruled Spain and Austria-Hungary (which also has a complicated relationship with the HRE).
Bangladesh, Taiwan, south-korea, rwanda and the netherlands and india are wayyyy more crowded than china. (bangladesh is ridiculously high, above 1150 (pop/km²), the others are approx 400-650 while china does not even reach 150. China is sort of between greece and switzerland when it comes to crowdedness (population density).