Wow,,,I've been ab diving since '74 and have never had the experiance you had on your first time....we did put a diver out one time while free diving for ab's but it was a scuba diver and alcohol was involved..
The kelp is thicker up north..I always carry a knife and have never had a problem, more than the kelp I worry about fishing line...one time while diving we had a commercial fisherman that caught live fish for the asian resturants come in on a kayak while we were down and surround us with hanging lines and hooks...
I did have one experiance of getting hung on the kelp while surfacing...I was less than 4' from the surface when I suddenly came to a screeching halt...I could almost touch the fin of my partner on the surface..the kelp had firmly wrapped itself around my fin strap and was holding me under...I was getting ready to remove the fin when it broke...
Also,,you can quickly cut kelp by biting it with your teeth,,,try this in monterey sometime...but if your caught in fishing line you'll have to cut it...
You and your friend did a great job...it was probally too late by the time you even arrive at the diver underwater...but you didn't give up and did everything within your power to help...God Bless you both...don't torture youselves with "what if's"...