Mongo has always had semantics to support normalized data modeling, has schema support, and has had distributed multi-document ACID transactions since 2019 [1]. You don't have to use those features as they're opt-in, but they're there.
I know that full parity between the two isn't feasible, but to say they never can is a mischaracterization.
[1] Small addendum on this: Jepsen highlighted some issues with their implementation of snapshot isolation and some rightful gripes about poor default config settings and wonky API (you need to specify snapshot read concern on all queries in conjunction with majority write concern, which isnt highlighted in some docs). But with the right config, their only throat clearing was whether snapshot isolation was "full ACID", which would apply to postgres as well given they use the same model.
