I always consider it against Spirit. She is the most unfun killer too fight in the game, and I always get destroyed by her, not because of skill, but because it's always a coin flip if I'm actually mindgaming her or not. And once you add Prayer Beads and Activation Time on it, it's just a chore and always makes me go back too killer.
Slow Down Freddies are annoying, but as a Freddy main at red ranks, it's kinda necessary. If you don't bring 80 things too stop gen speeds you're gonna get gen rushed 9/10, so I never blame a Freddy for doing it, because otherwise the game ends in 3 minutes.
It's true, it often comes down to builds more than an individual perk/item/add on that determines something is unbalanced.
Is Iridescent Head OP? No, not really. Is the fact that it stacks with Infantry Belt OP? Yeah.
The thing is, there hasn't really been anything that stacks up so heavily on the killer side in a REALLY long time. For the first time, stacking progressively building slows is actually a viable option over something like Ruin.
The issue is that people are taking this as permission to DC or give up because they don't like that perks make their objective take longer, and yet killer have been dealing with 90% of survivor running builds of 4 extra-hit perks in every single match for years, making THEIR objectives take longer.