Making form fitting boob armor makes the armor less protective and practically useless in real combat. Fact.
Not really. Long as it's not punctured, you are always just better off having armor on, no matter the shape. If it does get punctured, then you are SOL regardless because it got punctured. Shape of the armor really only matters regarding protection when the penetration and deflection capacity are at neck to neck so the shape gives you a slight edge, but realistically neither side of the conflict are using tech that barely work against each other.
The real reason for not making form fitting boob armor is that it's just obnoxious to make. It's bad enough to make one lump of metal fit the body, but now you are making armor with two lumps with less margin for error in dimensions.