This is just a flat out dumb idea.
There is a reason why pretty much every class has a core item that they build first, because most of that roster benefits from that item the most. Gives them early stats that they need, and buffs the champion much more than most other items can do. If you could ban these items, then this leaves many classes failing to have a good powerspike, and thus render them very bad. Take Irelia for example, Triforce is a much more important and beneficial item than Titanic would ever be. Let's say you decide to queue up for a game of league of legends ranked, and then both teams ends up banning items. I'm going with the extreme here and assuming that both teams end up banning the same exact items, most likely core items such as
. With the banning of ludens, that essentially guts
. Well, some of these champions can still be relevant building archangels, but oh wait, thats banned too. There's also the archangels users that we must now render useless as well,
(Granted, Ezreal can also go back to usual build of single tear, but he loses out in a lot of power without archangels). Are you seeing the problem here? Just by banning 2 items 31 champions are rendered near useless as they rely so much on that certain item to powerspike. That's 21% of the champion roster, aka 1/5 of all champions unusable. And many mage mains also play other mages so saying "Play another role" isn't a solution. With the banning of infinity edge, essentially all crit ADC's lose one of the best items they have, making them 50x worse than ADC's that don't require crit such as Vayne, lucian, ez. There goes another 10-15 champion. Triforce is a little more flexible as many bruisers that build triforce build black cleaver, but they also become weaker with Black Cleaver build, and some can't do that at all such as gangplank, rendering another 10-15 champions useless. Duskblade is also the same boat, youmuu's and duskblade are pretty interchangable for first item, but when you get to second item it becomes a lot worse as one without the other is a lot worse for most assassins than you think, and they also lose on a ton of late game power, making another 10-15 champions unviable. And this is only the one rare extreme case in both teams banned same items, most likely you will see the banning of other certain core items, such as black cleaver, bork, or protobelt. Now that means more than 50% of the champiosn in the game become a lot, lot weaker, and many players are left with nothing that can comfortably play, along with Riot having to deal with a balancing nightmare of who's too strong one all core items are gone. This idea will never work until we double or triple amount of items in the game so each class has multiple options for starting items.