That makes sense it's more that from first principles when exploring the options it looked like and I see below based on the public page, it wasn't even contemplated.. instead various key value stores without transactionality, and with eventual consistency and limited secondary indexing capabilities were looked at that are not widely used.
I guess my deeper point is there's sort of the illusion of a comprehensive analysis in the post when actually engines that haven't been widely used in 5-10 years were analyzed when more widely deployed engines weren't even analyzd that's what was odd