Unfortunately, it is not that simple. As you mentioned, both OSM and Google have significantly better values and both of them should be used for the source of the elevation in PGC.
The FAQ already mentions, that PGC does not do manual updates, but the real question is why the elevation is wrong, when the source is good.
There already were many similar question, since the change in November 2017, which should improve the things. But the elevation update was either not run for these caches (yet) or there is some bigger problem in the infrastructure, so I believe this is better to fill a support ticket, linking this thread. They might be able to reschedule the job to pull a correct elevation for your cache.