Legacy is a subset of modern, as such, if this fits modern, it fits Legacy.
Main features of a modern helmet are thus: T shape visor, front brow, rear brow band, keyslots, cheeks indented, ears in some form (RF are optional).
You can adjust a few of these without losing the modern look - the smaller the parts the more you can change. You can also add to a helmet - but it is then suggested that you start from a full base so you do not end up too far away from Mandalorian or modern.
If you look at most canon helmets they follow the same pattern of just changing one or two aspects but keeping the rest there.
As such, I see no reason why this is not a perfectly acceptable modern helmet. The rear brow band has been dropped which is a minor change. And potentially no keyslots, which again is a minor change if they have been left out.