Ivern is a very strong pick, no doubt about that. But he's just one of those well-designed champions that, even when they are overtuned, you do not mind going against one.
Jhin is another instance of this. Top-tier ADC for ages, but everybody just loves him, and I can't blame them. He's fairly designed, straightfoward, has clear strengths weaknesses, and his theme is just lovely. Could use some tuning to bring them down a notch, but they are healthy champions (or considered so) at their core.
Somebody like Garen, when strong, is not fun to go against at all. He'll just charge up your ass with his superior stats. His level 100 armor and weapon set is too powerful to fight against, he's like an RPG paladin. I do still play Garen, though. While his gameplay his boring, you have to admit his visuals are glorious, especially the execute.