There never was a lot of westcoast labels. Most of the majors were based back east, most of the hip hop imprints were back east. In Los Angeles there was Priority, Deathrow, Ruthless, Capitol and Delicious. Delicious wasn't a gangsta rap label they put out Young MC and Pharcyde records. Priority had Cube and Ras Kass (fukked him over a bit), few others here and there but ended up being merged into Capitol. Once the 'all star' team blew up everyone went their own ways instead of say all going over to Aftermath.
Kurupt ran to Antra...
Warren G and WC were already signed to Def Jam...
Snoop left to No Limit which was a Priority sub anyways...
Deathrow ended up stalling out Nate Dogg and Crooked I to where they ended up doing very little...
So to answer your question, Deathrow and Ruthless were the only gangsta rap minded labels and they ended up both being killed by Deathrow/Suge Knight....
Aftermath put out Game and Xzibit (platinum artists) just for the record...not to mention when Snoop, Kurupt, and Nate Dogg all went back to working with Dre/Aftermath/Deathrow 2.0 they started to make bigger records.