An opinion on cooldown items
This may be an unpopular opinion but I think the game would be a lot easier to balance if items didn't give cooldown. Champions would then be using their abilities with their intended cooldowns and it would make balance a lot easier for Riot to achieve, especially for mages. I know we are really used to cooldown being available to buy but if you think about it, it causes a lot of problems when some champs HAVE to buy it early because they have to be permahealing/peeling like supports or stacking like Nasus/Veigar/Cho. It hinders people from being able to actually get items to help with other areas of the game.
The other issue is that cooldown doesn't stack with the same item, which is strange. If you buy two bf swords, you get the accumulated amount of damage. If you buy two cooldown items or the same sort, you only get the cooldown from one of them, despite the fact it is a passive stat like attack speed, health or damage. I assume this was done as a half solution to not having too much cooldown available early on but it shows how it is a problem when it comes to items. If cooldown was removed, I assume many champs would have buffs to their cooldown times and everything would be in a better state overall. You would also have more people interested in playing support because of a wider variety of builds.