Well, most people like the LS because it looks cool, and don't care if it is historical or not. The reason I ask about LS is not because I want every soldier to look cool. I am asking if it is simply plausible to depict the fact that the LS is not widespread, but it was used by the Romans in limited amount.

I thought that with M2TW, it might be plausible to depict scneario where 1-2 cohorts wore LS, while others simply wore chain mail. It allows you to immerse yourself in battles, where some of your veteran cohorts managed to get the good stuff, while the more junior cohorts gets the normal stuff.