The phono stage in your vintage Marantz is typical of a basic MM 47k phono preamp common back in the day because MM cartridges were all the we had. So neither good nor bad when compared to another back then - just typical. It's another story compared to what we have available today with external phono stages.
A phono preamps primary job is to re-equalize RIAA and do so as quietly as possible. They all do the former but not the latter. Here is a little test...turn on your receiver and select the phono input. Do you hear any hiss or a slight buzz before signal without your ears pressed against the speaker? If so, its not very quiet. A good phono stage will be graveyard quiet before signal allowing the music to flow from a black background. And there a lot of very quiet phono stages available today for a lot less then you think that will be much better than what's in your Marantz.