I'm sure these stats are pretty reflective of reality, but it should be noted that a lot of non-custodial solutions for lightning addresses (eg, LNBits, satdress, etc) don't currently support the sending of zap notes (kind 9735) which might then causes zaps to be under-reported for non-custodial. I'm currently using Ligess for my setup which only started supporting Nostr zap notes a couple weeks ago.