the tech is meaningless. hawkeye can shoot regular arrows at his army and still kill them. they die by comventional hand guns. they die by a shield being tossed. and those are done by humans who tire.
i think y'all are over estimating how powerful thanos is. he was losing so badly to wanda he called in an artilery strike on everything just so he could get away. he needed the power stone to just beat marvel. he isnt that strong, they just made iron man and thor even weaker for fan service reasons. like, lets say its just the night king vs thanos with no stones and no armies. the night king is known to freeze basically anything it touches, thanos sword would shatter because its frozen solid and so would thanos. you also have the fact the night king is comparable in speed to cap so hed have no problem keeping up. the night king also doesnt tire plus seems to be immune to anything that isnt dragonglass near a godwood. thanos is gonna lose to general fatigue. if you want to add in space armadas then its kind of a coin toss because one death = another member for the night king as his ressurection seems to not have a range or require sight of bodies to be used. given the night king only has 1 weakness, its gonna almost always be team night king. lets say his frost dragon kills one of the flying things, he now has a flying thing.
i think you guys are underestimating just how useful unlimited undead raising and immortality is.