Then I wouldn't want to be in the skin of someone who's up against Oathbound mixed with, let's say, Vanguard who rely on ranged weapons. Then I believe this would really be a death sentence, unless I'm missing something here. However I get a feeling, that a single Seer unit with Fatalism combined with a bunch of ranged units, could really mess up at least a key unit in an enemy stack. I wonder how this will workout.
It's hard to truly say, it's just my opinion but I'm not a particularly skilled player either. Thinking more on it it may not be that insane for ranged. However what I noticed is the debuff remove all resistances which I think may be the more powerful thing to consider.
Depending on what you play, accuracy may not always be a problem (nor add to that much) so it's more a nice bonus, but able to consistently apply any effects to units with high resistances may be what makes it more powerful later on, and not necessarily unit deleting powerful, but if you do it right you can negate a fairly powerful unit from the enemy's side from acting.
To understand why the dev choose this, you have to go back way into the past.
The oathbound is certainly space archons, the vanguard is space human. Back then in AoW 1 and 2, there are both human and archon, by your point of view, these two races are overlapping. But if you actually play them, try to feel the immersion, human and archon is very different. I cannot say that it will be the same with the vanguard and oathbound because obviously none of us have played with it yet, but i have a feeling they will be similar to human and archon in that they are different as in not overlapping. Aside from them, worthy of mention is the azracs, this too are offshoots of human, yet they are different.
I mean, I can understand where they're getting at. If we only had Vanguard and now got Oathbound, I'd fully agree, but we've also got Amazons and Syndicate. Dvar and Assembly, whilst originally human (and Dvar just shorter humans), I'd feel they're distinct enough. Amazons, whilst they're sorta meant to cover muscular elves in a way, are still mostly just big muscular human women, but I'd still say they're also unique enough like Dvar. Dvar just get an edge due to we never seeing them outside their suit and you can easily forget what they are.
Syndicate however, whilst you can be blue skinned, are pretty much a human faction, a more sci-fi one compared to Vanguard. So then you got normal bit futuristic military humans, sci-fi/advanced tech humans and then Oathbound, which are extreme sci-fi/advance tech humans. So kinda cake on a cake with the last one, such as there were humans and archons, but also something inbetween or above archons.
Then the fact in the paladin aspirant's lore snippet it suggests to have lots of Vanguard members in it (as opposed to Syndicate which makes it more clear it's its own isolated faction and society, although there could be Vanguard indentured) who seems to agree Oathbound is better than Vanguard, whilst there doesn't seem to be any big lore hints about anyone going from Vanguard to Syndicate or vice versa, as far as I know.
Whilst you can imagine that in smaller instances, the human factions may have members switching sides, such as someone in Vanguard may choose "heck, becoming a cyborg sounds great!" and join Assembly, but they're small enough to not be mentioned much. Whilst Oathbound makes it clear it makes up of members from another faction as its backbone, enough that it's a unit's lore, and I do kinda wish myself it'd been more clear it was its own separate human isolated society until now and it'd be too soon for anyone to switch over, rather than appearing almost as if this is an evolution of Vanguard after time, even if it isn't.
But that's my only pet peeve so far and their campaign could reflect more light on it, otherwise I love the faction and got little to no problem them being human.