I'm looking for;
high density per km, lots of friendability population, reasonable architecture, good infrastructure, sunshine, tees and shorts living, vegan fitness, non-alcoholic/drug based fun.
high density per KM;
Most of So Cal is crammed with suburban tracts wedged between strip malls, with the occasional city center highrise buildings. But I think in the areas you mention it's a little more spread out.
lots of friendability population;
Most people are friendly
reasonable architecture
not sure about this. They have buildings. Mostly modern stuff, I'd say.
good infrastructure
First rate as far as fixed improvements. For transportation, you can drive anywhere if you have the time as roads are everywhere. I think public transit may not be up to what you're used to, but it's not bad.
sunshine
Yes. California is in a drought. When it rains you will probably have floods!!
tees and shorts living
Pretty much yes. The climate is mild.
vegan fitness
I think this is pretty common in So Cal. especially in the communities you list. Maybe others can comment. Here in Northern California I've noticed the typical person has become a little larger.Sadly, obesity is more the norm.
non-alcoholic/drug based fun.
Maybe locals in SM are into this, but ime, all of So Cal is one big party with plenty of drugs and drinking. Not for me any more.
I have to comment that with your username, I'm surprised at the gentle, optimistic, life-loving, holistic-health tone of your post.
If you really want a good place to live, go to Hawaii. The only drawback is the cost, but if you can afford SM, most places in Hawaii are in rich, and still plenty of haole souls to harvest, lol.