This is true, but it doesn't compensate for their abysmally low IS matriculation rate. Their OOS matriculation rate is a very respectable 23.4%, which is far above the national average of 16.6%, but this is more than erased by their 17.2% IS matriculation rate, which is far below the national average of 25.3%.
Overall, there are worse places to come from than CA, but not many. Also, due to the extremely large size of CA and their generally crappy numbers, no state has more applicants fail to matriculate anywhere than CA, including TX. By a lot. CA had 3,946 applicants fail to matriculate in the latest reporting year. TX was the runner up at 3,036. After that, the next highest was FL at 2,279.
It is what it is if you have no choice, and being from CA does confer some benefit if you are shooting for CA schools, but, overall, applying from CA is a significant disadvantage that almost 4,000 people fail to overcome each year. That number is sure to be much higher now, given the surge in applicants over the past two cycles.