First let me begin by clearly stating that I am not an instructor.
You certainly had a bad experience, and there is plenty of blame to go around. You have already owned up to your own mistakes, and you have clearly learned many valuable lessons from this experience. The instructor appears to also have made some poor choices. The instructor was however looking at you and the other students as certified divers who were seeking additional instruction, and not unskilled divers. This is an important distinction, but does not remove the instructor from blame.
I think that the biggest mistake you made was an honest one. You failed to fully appreciate the ramifications of diving in the cool Pacific. The visibility and water temperature here can really change your perception of what diving is. It slows your thought processes, and the thicker thermal protection makes motor skills far more challenging. The rental gear is a factor, and you have been pretty clear about how it affected you when you were in the water, but you did have time on the surface to make yourself aware of how it worked.
Don't be afraid of diving here in Southern California or anywhere else for that matter, but do make little steps, not big leaps. One of the more controlled environments in Southern California is the underwater park in Avalon on Catalina Island. The water temperature is the same as the temperatures elsewhere in the area, but the visibility is usually better, and the shore entry is about as simple as it gets. Walk down the steps and wade in to the park. There are a few rocks at the bottom of the steps but they can be easily negociated.
After your experience you have posted above I would encourage you to take an easy dive, possibly even an instructor guided dive at the underwater park. This will serve to help you to regain some confidence and aquaint you with the diving conditions in Southern California. The first time you remove your mask in cold water you are in for a shock so practice this skill in a controlled environment like the park.
You do not need to buy your own gear, but you do need to be familiar with your rental gear. You also need to be willing to refuse rental gear that you are not comfortable with. This is part of the philosophy of being willing to end the dive at any time. In the case of refusing rental gear, you would end the dive long before you even get near the water.
You appear to be well on the way to learning from this bad experience and not being overwhelmed by it, so my compliments to you. Learn from this, make a vow to never make these mistakes again, think all the way through the problems. Remember, if you are lower on air than you want to be and you feel that the dive is over but your buddy does not understand, you need to make them understand. They may be narced, grab them and get close, don't let them ignore you.
Best wishes for safe diving in the future,
Mark Vlahos