I think the point was to show that Mamoru is a right douchewaffle. They succeeded. But before we pass blame around, at this point in time neither of them were super mature characters anyway. It's hard to forget but Sailor Moon R somehow plays concurrently to Sailor Moon (no other way Usagi can stay 14 for two years unless they weren't reincarnated as much as there was a time-reset where for some reason they and Luna kept their memories, but perhaps I am overthinking that). Talking it out would have been the mature approach.
You're right, Ami was the most popular character of Sailor Moon by far, at least in Japan. I think in the West that might have been Makoto (also Malcador's favorite), but Makoto comes without the burden of all the cultural issues she represents for us (it's not just that she's tall, she also wears long skirts and has wavy hair, everything that's not normal for Japanese women, and it stands in the way of achieving her dreams so much). Poor girl.
Not gonna lie (and as I already mentioned that in the metal thread anyway):
But Ami represents much, much more than that for me, and it's mostly identification and not "I like what they've done with the character", although admittedly I am looking at this from a perspective of having seen the entire run (mostly, apparently, because I definitely missed some SuperS stuff). I might go into more detail on that later (if any of you are really interested, but that's going to become super long winded and might up reading as if I'm trying to come across as... better than I am? I don't know..., it's also probably better served as PM, but hey, uhm, what... completely lost track of what I wanted to type here), but today's super busy. Man, if there's one thing I miss about school - and that's not a whole lot, to be honest - it's having f*ck all responsibilities and virtually endless free time. Meh.