It wasn't even about sticking power. It was about the RNG perma-slow.
It made trading in lane very binary and solely up to RNG and the inevitable stat-check that followed.
It was the RNG and stat-check that made the slow an issue.
What are Gnar and Yasuo really good at? Stat-checking. This is part of why they do so well with Frozen Mallet while others do not.
If it was just based on stickiness/stat check on non-overloaded champs, you'd think Irelia, Jax, or even the borderline overloaded champs like Fiora would buy it.
Its not about how sticky the champion is before Frozen Mallet. Its about how oppressive/ungated they are once in range. Gnar/Yasuo have essentially no gating and are extremely oppressive when you can't just turn and kill them right away.