jackal

One, weather is virtually never an issue at LAX. The separation requirements only apply during ILS landings. Visual approaches (used almost 100% of the time when weather conditions allow, which is virtually 100% of the time at LAX) have no such restrictions.

Two, the immediately-adjacent runways at LAX are never used simultaneously for approaches, either in good or bad weather. For each of the two pairs of runways (24L/R and 25L/R), one is used for take-offs and one is used for landings. Thus, the factor that they are only ~700 feet apart is immaterial, since the fact that all four can't be used for simultaneous landings means nothing as all four never are used for simultaneous landings, and since the two runways most typically used for landings (24R and 25L) meet the standard separation requirements, and in the [extremely rare] event that weather is an issue at LAX, LAX can continue to accept inbound aircraft at a normal rate.

SFO relies on its two parallel runways (which are far less than the required 4,300 feet apart) to accept all inbound aircraft, in both good and bad weather. These runways are too close to conduct parallel ILS approaches, and so when the ceilings are low enough to prevent visual approaches, the arrival rate at SFO is cut virtually in half. That's what causes the delays SFO is infamous for.

The SFO airport has actually crafted a pretty good overview of the issue (meant mostly for clueless media types to be able to try to accurately report on it, but it's helpful for all interested folks).