What are the disadvantages of heavier armour (other than the missed bonus from cat/griffin school techniques general abilities)?
The weight of your armour affects the rate at which your stamina regenerates.
So heavier armour, despite providing more damage resistance will prevent you using signs as frequently. Wearing lighter armour will not penalise your stamina regeneration, so you can use more signs.
Armor weight class effects Stamina regen.
Light armor: bonus to stam regen Medium/ no armor: normal stam regen Heavy armor: penalty to stam regen
FWIW, the crafted armor sets have the same raw armor values at mastercrafted (save the wolf set, in that I don't know for sure that's true, not that it isn't true), so by level 30+ the question becomes which perk and corresponding armor set are best suited to your play style. You'll also have so much alcohol you'll be able to use tawny owl on cool down, so stamina ceases to be a concern.