“Rav Moshe argued (O.C. 4:88) that since Brooklyn is a large city and some my think that it contains shishim ribo, one should not establish an eruv ”
This again is only in reference to “establishing” an eruv not once it has been established. No?
Nev,
“The question is, is LA comparable to KGH (matir’d by Reb Moshe) or to Brooklyn ”
Define the difference and you might have the answer.
In any case, as I have posted above, it may very well be diff, due to the factor of not having the amount within 12 Mil x 12 Mil, which is a major factor of Rav Moshe’s issur.