Swimming: Swimming seems very dangerous in the low season when it is windy. Again NaiYang looks safest. Do not ignore red flags. Most beaches have no life guards. Seen reports about elite sportsmen almost drowning .
I don't think it makes sense to consider swimming separately from kiting, and decide that kiting is OK but swimming is too dangerous. If you think it is very dangerous to swim in a given spot, what are you doing kiting there?
Your starting assumption while kiting has to be that you at any moment could end up completely separated from your gear and have to swim back to shore (unless you've got a buddy on a boat or jetski looking out for you, of course). Don't be out there if you are uncomfortable with that idea.
I agree with the rest of the stuff you wrote, about the spots. The northernmost section of Karon beach can get a decently well-organized shorebreak. It can be dumping at times, but not that big though. The biggest waves I've personally seen at Phuket was an overhead shorebreak at Kata Noi.
Yes, right, kiting, especially alone where you would not swim seems irrational. You have to consider the possibility of having to swim when you kitesurf. I know some thai kite surfers ask the boat guys to look after them. Perhaps some tip for looking plus big reward in case of a rescue.
Some beaches seem worse than other. You have to prepare for the possibility of a swim and avoid bad spots. Had a busted kite on a couple occasions. First time I had a tough swim (not in Phuket). Second time another kite surfer could tow me in. (I have now bought a new kite). Don't kite alone, too far from other surfers not too far from shore when the red flag is up. If you have to swim - stay calm if currents. Swim sideways to get out of rip at the end of the beach where water is going out. Take breaks when you get tired. Swim on your back for a bit. Etc etc. It is easier to handle the situation if prepared.
Would be great to exchange spots and ideas where to surf in another thread.