well Boku goes out of its way to focus on things like: bureaucracy, and even though it has a main character goes out of its way to make time for side characters and the like to a MUCH greater extent then FMA does. don't get me wrong i love fma, i think brotherhood is one of the greatest anime of all time and goes a long way in portraying the human condition in times of war but at the same time, its got flaws that Boku doesn't. if fma were kmore like Boku, for example, we'd have gotten more focus on such things as how all became an official alchemist in the first place as well as the work they actually do. but from what the series give us it leaves some glaring holes in the entire process such as how the entire general process works, how they get paid for they're services, how al lives his day to day life outside of the exciting parts, how different alchemists interact with each other, the technology of the time period outside of weapons and the likes, ect. Boku hits all these points, and does so in such a way that it immerses you in the world to the point where you can actually imagine yourself living there. hell, vigilantes takes it a step further and goes on to portray life outside of the law and establishes norm by showing us the day to day lives of characters we'd otherwise never get to see in the day to day lives of the hero's like Deku.
sure, you can argue that there's genuine realism in fma, but not to the same extent there is in Boku. that's just a fact.
Eh, this has nothing to do with being realistic. You just have a crave for slice-of-life-ish details, which, yes, contributes to realistic feel but that doesn't mean every show has to do it to be called realistic especially if the focus of the show isn't about such thing. Real life has several aspects, yes? And there's only so much a show can address. Being selective is a thing.
Boku can afford to do so because of its setting. On the other hand I can just say Boku hasn't done anything about war like FMA...