I honeslty believe items like Rylais and Frozen Mallet in their current forms are unhealthy

One of the biggest reasons for this is because nobody likes being perma slowed just because another champion is within range of them. The other thing is, both of these items take out the skills of the champions who build them. Rylais makes landing skill shots 10x easier, Frozen Mallet literally makes the most inept mechanical player able to orb walk like a god (for both chasing and kiting). Having passive slows simply for existing is a bad thing and both of the items are hot topics as of late.

Anyone who has an issue with one but doesn't have an issue with the other is completely hypocritical and bias by the way. Yes there are cases where Rylais isn't a problem on champions, yes there's cases where Frozen Mallet isn't a problem on champions but regardless, even in those cases the gameplay both items encourage is incredibly unhealthy. I would much rather see the items have slows that eventually decay or fall off entirely after a certain amount of slows or have the slows become temporary actives, though in fairness we have tons of active items already so maybe that's not such a good idea.

Do it riot, change the items while you still can. Remember, you wanted to remove Frozen Mallet at one point and while it was probably because the item wasn't considered good, I also believe you know a perma slowing item isn't exactly healthy. And the same applies to Rylais.