A great feature of pydantic are the validation hooks that let you intercept serialization/deserialization of specific fields and augment behavior.

For example if you are querying a DB that returns a column as a JSON string, trivial with Pydantic to json parse the column are part of deser with an annotation.

Pydantic is definitely slower and not a 'zero cost abstraction', but you do get a lot for it.

msgspec is much more memory efficient out of the box, yes. Also quite fast.

Can it do incremental parsing? Cant tell from a brief look.