Go look at some medieval codpieces (ntm the tight waists as was attractive back in those times for males) and tell me that doesn't suspend your disbelief. Then, have a look at greek/Roman-fitted armor, where they have toned muscles engraved on the breastplate. Armor has been used in the past to sexualised the wearers, it just got more expensive over the years due to improved forging techniques, and the fact that it's quite hard to shape mail armor. Given how Mandalorian armor is based on spartan culture, and the warriors of such had periods where their standard armor was form-fitting and made to sexualise the wearer (in those times, primary males), then there should be no issue with a slight protrusion for females that look far more practical than sexualising. Mando's armor is made to fit his form a lot more closely, with a clearly-defined breastplate