Ok, as much as I don't like it when it comes to squishy classes, each class has an item that gives them some way to combat their weakness. The key is that it can't be so strong that it makes their weaknesses non existent.
Take thornmail for tanks. By design it punishes sustained damage, which is what tanks are weak against. But if it's too powerful, then it pretty much removes a gameplay weakness from tanks, making them unfair to fight.
Juggernauts have items that allow them to be extra sticky, but FM isn't going to stop dashes from Lucian. If you gave juggernauts access to an item with the grounded effect though, then they'd be impossible to escape and fight from.
Now ranged champions I agree will abuse this factor. They have access to pretty much anything they need to counteract their weaknesses and make their strengths better. I don't like that honestly, so I won't disagree that ranged champions don't seem like they are really sacrificing anything for all the advantages they have (even if they are squishy, they have enough tools to evade or survive a burst rotation. So ADCs might be pretty powerful in the preseason if the reworked assassins can't take them out).
IMO the key to balancing items and classes is that their benefits must not make the class weakness irrelevant. That's why I hated tank assassin builds because despite the damage they sacrificed they still did their job effectively. Hell, they did it better.