Aren’t some homes in this area already in the 300’s?

Not in this specific neighborhood. Some homes in 92126 are, but this area is considerably newer than most of 92126 (built in 1989 as opposed to early 70’s). Better comparison is vs. 92121 (Sorrento Valley) or south 92129 (RP south of 56) and you’ll have a hard time finding a 4br house there for less than 600k.