After watching the stream I'm kinda wary about Curse of Fatalism: 3 turn cooldown to ensure an enemy unit is hit by every attack and affected by every malus for two turns sounds really powerful. I understand that Oathbound are mostly melee and some weak range units, but what's stopping you from getting range NPC units or units from other races? Even in the stream, Tom mentioned that the paragon soldiers have a chance to stun when overcharged and with fatalism, the stun is ensured. This can easily stop a tier IV unit for a few turns with a Tier I unit.
I do share some of this concern. Especially if it is used at the ' top of the round' in conjunction with ranged units.
Then again, setting this up would require considerable investment on the Oathbound player's side; you must build specifically for wardens (which I expect will not be a ' top tier' ranged unit for its cost) or get another faction good at ranged strikes (Vangaurd for example) or invest in native units (such as Paragon). Specializing in this way might give this player a strong tactical game centered around the Curse, but is also counterable on a strategic level.
For example, the stacks used in the stream are extremely slow, hampered by difficult terrain. The Augur itself is not, but is probably (as said above) not a strong massed floater unit.
The concern that the use of the curse leaves no tactical counter (such as removing the debuff through operations, abilities or counters) remains. On the other hand, it does not influence action economy or movement and might be resisted outright(which consumes the Augurs move and repeating attack with it).