A bruiser will not take over a game relative to a mage atm unless they get extremely far ahead or the entire enemy team is AD/low CC. Being melee is a crippling weakness in this game that you can only overcome by being an overloaded champ, getting far ahead, or your enemy being stupid and going absolutely glass cannon.
A bruiser must build sunfire, IBG, or TF in order to be both tanky and deal damage, none of which help much vs magic damage.
If a mage is kiting, the mage will easily win. Rylai's makes that significantly easier, and makes immobile melees non-viable in most cases.
**A melee permaslow does not make anything non-viable. It means vision and positioning become more valuable. ** The exceptions only come in when you add mobility as a factor. Just like Ashe's permaslow in season 1, mobility (in the form of dashes/blinks) has swayed the dynamic of game interactions an absurd amount to the point where you have to have very specific tools to function now.
What's the difference between an assassin killing you instantly and a bruiser taking 5-10 seconds to do so, where your team could come and help? I'd say the perma-slowing bruiser is healthier, specifically if its only applicable to relatively immobile ones, such as Skarner in the past.