Most of the design choices are based around these RNG effects. Many things are 50% or 75% or 20% etc ...
Agree or disagree with the design, but people often joke about the game as RNG built on further RNG based on foundation of RNG.
The trick with winning in this RNG environment is to account for it and try to overpower it. In this particular case you want to outlast the Stoneskin and just wait it out though Stone or Block Damage or Unkillable, or use multiple champs to remove, so buff removal followed by buff removal, or use champs like Armanz and Wukong that sheep over it, or use very well built nukers that can break through it (a well built Ronda A2 does a good job of killing any Stoneskin nuker), or bomb them, or burn it off.
They want you to find other solutions besides just removing it, basically.