I agree there is a >99% chance there is no intent behind an online death threat in FAF but the optics are terrible.
League of Legends is famous for its toxicity and "kys" tagline. Despite it going pretty nuclear on toxicity it's still known for it. Same can be said for other games such as Counter Strike. You should moderate hard against this kind of stuff because a welcoming community is vital for retention and attraction. You also should moderate extra hard so such toxicity doesn't display itself in the pro-scene tournament finals - because pro-level gameplay in a competitive game is some of its core marketing material.
The same can be said of racial slurs. In the last 2 years I've seen on 3-4 occasions some of the more well known pros use "ni**er" in chat repeatedly as well as repeated use of the seraphim voice taunt "There can only be one superior race" (or however it goes). Even recently in a pro setons game I saw some teammates on voice comms and I assume a guy joined because one of them pm'ed the other (ingame) "wtf there's a ni**er in chat".
I'm as big as guy on free-speech as anyone but the optics here are frankly terrible and even if it happens 1 in 10,000 games it only takes exposure to a few incidents for FAF to get a reputation.