I think the issue here isn't just that stealth itself is a problem, but that it combines especially poorly with front-loaded damage. Season 8 is a season that has seen a large increase to the front-loading of damage, both through Runes Reforged and through the addition of items like Stormrazor. Additionally, it feels like damage itself has continually been raised, shortening the window of time any player has to react to being attacked. Because of this, I think the answer here should be to remove items and runes that front-load damage, and see where it leaves stealth champions. Up until recently, for example, Wukong felt pretty weak to most, but now he's a monster because he can abuse stealth to deal a huge amount of burst with an E + Duskblade Q + Ignite + Electrocute combo.