Is Fire Emblem 3 Houses the darkest Fire Emblem yet?

I have played only those games so far, which got a western release (or remake), and they always had a dark background story: Typically about war, invasion, sometimes genocide or the destruction of whole continents. But you were fighting this.

And there have been rather dark characters on your side, the crazy stalker (Tharja, a rather popular character, and Rhajat, who is a intended to be a very similar character btw), the swordman who enjoyed killing (Karel, but there were also others) and I would really like to forget Peri, who killed her servants (and obviously was allowed to do so by her parents) just to watch the blood flow.

The characters are partly child soldiers, but this is not unusual for Fire Emblem.

But as far as I remember, those have been some singular characters.

In 3 houses (heavy spoilers incoming!) you have several characters with massive trauma (two of the fanbase favorites are a paranoid recluse and a depressive girl with low self esteem and suicidal tendencies) and an Archbishop (and traumatized daughter of the creator god) executing people who rebell.

And then you have Sylvain. After the first look (and support conversation) you might think he is just a random philanderer, who does not care about women's feeling, but later he is forced to kill his brother and it becomes clear, that he disrespects women because everbody cares only about his supernatural crest (and not himself). In one of the last conversation you can have with him, he tells, that he always fights like he does not care whether he survives, and he is not going to change it.
So, who knows, who else is longing for the sweet release of death' embrace?

Oh, did I mention, every side commits war crimes? And with 4 different routes (+ DLC) you play as almost everybody sooner or later.

The most popular route, btw, is the one, where you start that war that engulfs the whole continent.

Again, heavy spoiler incoming, the whole war mostly happens, because there is a secret cabal in the background, who manipulates several characters, so this war is even more senseless than war in general is.

tl;dr: Yes, it is.