Leyland Cypress, fast growing

No, no, NO to Leyland cypress and especially in SoCal!! They get far too big for any residential garden and with far too many issues.

Frequently used plants for this purpose are fern pine (Podocarpus gracillor), Ficus nitida, ceanothus, California bay laurel, toyon, manzanita, Italian cypress and Indian hawthorn, Strawberry tree (Arbutus unedo) is another possibility.

Oh, sorry, we have them and have NO issues and line a fence for screening from neighbors! Although yes would need trimmed once a year, but BAD on me didn’t know about So Cal as live in Portland

IMO instaed of planting anything more why not just a trllis type topping to the wall Then if you wanted to later a vine or grapes would grow there probably .You do not have a huge yard so IMO I would not add anymore trees to the yard.I don't think you need anything huge since the neighbors really can't see into your yard anyway.

When I lived in San Diego I loved having dwarf citrus trees in the yard. My favorite was my citrus salad, had 5 types of citrus on one tree. The varieties I had grew to about 8'-10' high and wide.

It not only hid the fence, but provided fragrant flowers in the spring, fruit for the rest of the spring summer and deep into the fall and are attractive trees.

My neighbor had a Jacaranda in her back yard. loved the spring flowers and still attractive when not in bloom.

You also have a great climate for a climbing rose. I had climibing royal sunset rose that bloomed from April to November and was taller than my house.

Food plants. Citrus makes a great hedge and in time can be tall enough for privacy. If you need a single big tree, loquat (the eatin' type) or avocado are lovely.

Of course, actual location matters for what you can plant. I don't know if there is any half-a-state with more environmental variety than southern CA. The photos don't look like Baker or Arrowhead, though. :P

I actually like what you planted a lot. I think it will fill in and provide privacy from the neighbor. I would continue on and do the one replacement.