--snip--
It's obviously wrong, Ordinals TX has size more than 0.
I didn't say Ordinals transaction size isn't zero. I said technically it isn't a waste in block space. Why? Because the data isn't embedded within the structure where the UTXO set is stored. It goes to the structure of the block where witness data are stored, which is prunable.
1. While it's true you can prune witness data, AFAIK there's no full node which let you do that.
2. It's still waste of block size since Ordinals TX has size more than 0. Possibility of pruning witness data actually means it's not waste of storage space.
But Bitcoin Stamps is something different, and it should be more concerning in my opinion.
It's definitely more concerning, although it's easier to make such TX become non-standard.