bruiser and hypercarry aren't mutually exclusive
Your allied carries aren't going to shred him to bits like they would a Darius or Jax.
late game? yeah they would, gaining flat resists doesn't really help him against items like
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or true damage champions. as long as your team isn't scattered taking down a Nasus will still be easier than a Darius in the same scenario, since Darius has sustain scaling with himself and Nasus's lifestealing can still be reduced by defensive stats (he's also single target, so no chance of taking down multiple people at once like Darius or Illaoi)
you're probably not going to peel a Darius solo after he has DMP/Glory and Cleaver, especially not if he has stormraiders. Darius, like Nasus, will get beat up by enemy coordination and will require his team to coordinate to make them succeed in teamfights.
The only counterplay to Nasus was that he couldn't really threaten the front line overly much so they could peel him for the back line for long enough for your allies to win the fight.
counterplay to Nasus is to prevent him from getting stacked enough to threaten your tanks in the first place. as well as walking off of his E which will now have a much more significant impact on cutting Nasus's damage to you than it did before if you're building tanky
nasus is allowed to be tankier than trynd and fiora because he doesn't have the tools they do to avoid or negate incoming damage.