See, in theory, and at higher levels of play, I would agree with you. It's not hard to understand the concept behind Nasus's counter play. You mess up his farming, you keep him from getting stacks, and you eat him. GGWP.
In most realities, however, this doesn't work out as neatly.
In order to truly counter Nasus, you need someone with strong early game harass AND strong towerdiving potential (or at least hideous amounts of burst poke, because any Nasus worth their salt can farm and sustain off their passive under tower literally for free). Towerdiving save in a few cases without regular coordination from your jungler is suicide; Wither will quickly turn the tables or at least force a trade in his favor. Other than perhaps a Jayce or GP (or playing an assassin top lane instead), you can't REALLY shut down a Nasus.
Though I generally hate infinitely stacking abilities (they're essentially abilities that will eliminate any and all counterplay just with time), I'm not gonna get into that sticky argument. Instead, here's what I would suggest:
Change his passive.
The whole "scholar turned warrior" motif not being fulfilled aside (he could defoes use a mini-rework), his passive essentially makes his proported counterplay non-functional.
"It's alright, guys, I'll play a harass laner, like Kennen or Teemo!"
Lifesteals and farms under tower
...
If you compel Nasus to make the choice between having a splash of sustain and going full tank, you make his intended counter play more viable while also helping diversify his potential builds.
I'm a silver scrub, I know, but that's just my take on it.
Also, anyone who's willing to give their input on the following, I'd really appreciate it:
https://boards.na.leagueoflegends.com/en/c/skin-champion-concepts/2JZY9zza-ultimate-champion-skin-concept-celestial-lord-taric