The cover art archive servers seem not particularly fast, at least compared to cover art providers such as Apple Music or Bandcamp (429 pretty often though).

Downloads can be quite the pain already. If possible multiple images should be uploaded simultaneously.
This won't help much with digital releases where there is often just a single cover art however physical releases with multi-page booklet scans and everything else the packaging holds could greatly benefit from it.

The actual edits are not always immediately created, it can take several seconds. In that regard multiple uploads might also reduce the waiting time.