They're not "notoriously difficult to enforce", they're specifically unenforcable to non-executives. The CA legislature and judiciary have long since settled any questions regarding these and also have frameworks in place for companies trying to make you an "executive engineer" or "director of blah" to try and get around it.
Yes, and CA really doesn't want non-compete clauses, so they invalidate the severability clause as well.
By the way, the Silicon Valley HBO show can be remarkably accurate on things. It's rare that a TV show gets things like this right, where people in the business don't.
I just happen to know lots of attorneys in the space. I am not an attorney or giving legal advice. Talk to your attorney for that.