I’m gunna say ‘historical’ for msg. In the original version (way back), it was the only field. The goal at that point was to build towards what we have now with the payload with the object result type (even the numUids might not be needed if we had aggregations in there).
In general numUids == length of results array. But you can of course filter that array, so sometimes it’s helpful to have both. I think the “Deleted” or not is as per @amaster507 suggested and is just the number of things that got mutated, e.g
There is are subtleties here cause the number of things that can be returned might be different to the total number of things matched in the filter or mutated cause of auth (e.g. if the delete and query rules don’t equal the same things).
I don’t see a problem with removing it … but there could be cases where you want to return some more info in all the payloads of all the mutations.