Basically all his utility can negate different strenghs from killjoy
Viper Orb doesnt have as much impact cuz you can protect your team from spamming with ISO WALL.
You can cancel Viper's Ult by getting her in your own ult.
You can "equalize" spamming by making her fragile too, which means you can disrespect her snake bite more often.
If the site is very closed off for entry (cuz of orb, wall, and molly) you can 1v1 viper without knowing exactly where she is.
With all that being said
ISO will not have value if the enemy viper is one of the following players:
Less
Pancada
Suygetsu
Mako
Mindfreak (the lawyers of tiktok have advised me to disregard mindfreak 😭)