Funny you use amumu and malphite as examples, because they’re two of the few champions that don’t get fully negated by banshee’s. They’re right there on top of you after their engage. Banshee’s is better for stopping one off long ranged cc/de-incentivizing a burst combo on your champion. It’ll make a leblanc think twice. It’s not going to stop a tank or a diver from coming onto you.
And while I agree that tanks don’t have a need to stop engage as badly, they didn’t dislike banshee’s when it was a full tank item. Tanks too can be engaged upon and killed quickly in many situations. Not getting hit by an ashe arrow, or intentionally blocking an ashe arrow with a banshee’s, is a great example. Plus, there’s no reason why there shouldn’t be full tank items that are intended as a one off defensive item for other classes. Just like triforce is a one off offensive item for bruisers, the same can and should be true for some tank items, significantly limiting a carry or a bruiser’s damage if they decide to opt in for some of the best defensive passives in the game.
And while you bring up lethality, it’s worth noting that assassins of old had 100+ AD items that they could stack. The story didn’t magically change just because we swapped those with ~50 AD lethality items. Nowadays everyone, assassins included, is running GA if they can make use of the ad. Juggernauts, divers, ADCs, assassins. There is not veritable sacrifice because the GA passive, while limited in ways you mentioned, is good against all damage sources. In a time when scalings are higher than ever, the ad on GA is universally applicable to AD champions, and doesn’t limit their damage enough. Surviving longer is more damage, so the tradeoff for not getting another offensive item is minimal. The loss of risk and the suddenly increased difficulty of killing a GA champion makes it so that the GA user dies much less simply because of the lack of incentive to dive a champion that’s going to revive, let alone when they actually revive. A damage champion should have to trade off significant damage to procure that power.
I fail to see how GA doesn’t fit the tank thematic perfectly. It allows them to maximize their survival time and is a strategic item that can allow them to, in certain scenarios when it is off cooldown, fight a lot longer. I question whether tanks should be going after items that let them do more damage as opposed to items that allow them to live much longer to then do that damage.
I understand that it was game warping, but are you implying second and third item GAs on carries aren’t game warping? That every ad champion having a stop watch isn’t game warping? Please. When it was cheaper you’d see GA on EVERY AD champion that could get it. It’s the core of most bruisers alongside sterak’s, it makes yasuo, jax, camille, master yi, riven, and others bullshit to deal with. Sure, Jhin isn’t the one broken with it. Having to deal with a Vayne, Kai’sa, xayah, lucian, or ezreal that just come back after you have to get through their whole to kill them is just utter nonsense. Not the mention what broke tanks was that it revived them with 30% hp that was then augmented by spirit visage and healing increase runes. Nowadays it heal by a flat amount which is by far more ridiculous on low health damage dealers. It’s fine to keep that flat number, but make it not have AD so that damage dealers really have to sacrifice damage to get it.
Heck, make it augment damage after you revive for a short time, but only after you revive. Boom. You have an item made for damage dealers that is simultaneously not making them stronger at every moment of the game.
TL;DR: as it stands, GA makes every AD assassin much tankier and leads to a tanky damage dealer meta, making pure tanks and damage dealers that can’t make use of GA and similar tanky offensive items less worthwhile.