Oh, you didn’t mean ADS-B was imprecise but that the collection of ADS-B data is imprecise. Got it, and agree.
ADS-B, which I am perhaps a collection expert since I am a chief architect of data management systems involving ADS-B, is a short range radio signal, so it isn’t going to be picked up in every location. All kinds of tracking systems have been devised, even some you can buy for a personal computer, but it was never intended to be a wide area system.
There’s some pretty good info on this forum including a recording of the ATC communications.
The helicopter was on hold for 15 minutes waiting for traffic to clear around Van Nuys airport. He wanted to go VFR from that point on.
The 15 minute hold may have given him a case of get-there-itis.
https://www.pprune.org/rotorheads/629197-kobe-bryant-killed-s76-crash-3.html