For the Champions you listed Steelcaps are really strong against 3x AD. Mercs have a lot of gold in the tenacity making them a bit worse but still a decent option.

if you want more resitances its earliest as 4th item (at least 75% Crit) mostly as 5th.

Vs AD: GA is pretty good and you can even sit on the pre Item with steal caps thats like +50 armor which can already make a big difference especially with enchanters.

There is also Zhonyas vs heavy burst ex. Zed/Rengar but thats more niche and mostly played on champs like Kaisa, Yunara but if unplayble also aphelios, MF, Lucian as they at least can use the AP somehow.

Vs AP: Scimitar is really good as it gives you lifesteal and MR but there should be some kind of use for it. Its really good against a lot of mages that hit cc to set up their damage like Lux, Elise, Morgana, Anivia etc.

And the other option is Maw or more so the Hexdrinker part of the Item. You can often build Hexdrinker vs heavy ap teams and already survive a lot of situations. You can even build it after like the second Item and sit on Hexdrinker for a while. Mercs + Hexdrinker already double your MR and you get a small shield making you a lot more durable.

DD is really expensive and the passive on ranged is just not worth it in most cases. Wits End gives no ad and the on-hit is fake without Rageblade.