Isn't altitude information also one of the important things about ADS-B that radar lacks?

Although ADS-B is self reported and "vulnerable" to bad/spoofed info.

My CFI and I once saw ADS-B data from one of the startups near Palo Alto airport in California reporting supersonic speeds... at ground level, no less.

Edit: still have it in my email, heh. It was a Kitty Hawk Cora, N306XZ, reporting 933kts at 50'.

Civilian vs military. The military can get altitude information from primary radar.