You have mercenaries to deal with immunities. You can use followers in D3 TX so why can't you use them in D2 as well?
I'm very skeptical that every set can do TX like you said... I have been trying to mess around with a full Armor of Akkhan set Crusader for a while, and have had zero success even doing Bounties. There's no way I could kill something like Belial solo in TX, much less solo in a 4 player game. You can argue that I built this Crusader wrong, but even Blizzard realizes that this particular set blows.
Blizzard is giving the set a pretty significant buff in 2.4.2:
http://us.battle.net/d3/en/blog/20149714/patch-242-ptr-patch-notes-7-12-2016Like I said, going through TX is cute and all but TXIII is coming out in this next patch too. The bar will be raised, and honestly how many viable builds will remain viable in this higher difficulty? Do all sets remain viable? And even if they somehow did, it's 4 sets per class. Just in my Paladin example, I list 6 builds. And I'm sure I didn't even list them all.
If you continue to compare TX to D2's end game, you are only comparing D3's
mid game to Diablo 2's end game. It's really not a fair comparison here. Hell difficulty is the highest difficulty and the final destination to play in for D2. You literally can't play higher than that for experience or loot. There is a reason people bot their way to 99 in Hell difficulty Baal runs.
To make a fair comparison, you gotta compare D2's end game to D3's end game. Greater Rifts are the end game content for D3. Most players only do normal rifts as a source of keystones so they can participate in the actual end game content which are Greater Rifts. The higher you go in up in the GRs, the more loot, experience, and better gear you can get thanks to the whole legendary gem system they put in place. Running rifts in TX is really just mid game, especially considering most people can breeze through GR 70's now while TX is the same difficulty as GR 45...
And to make it fair, you need to ask how many builds are END GAME viable for each class. Or if you want to make it fair, you might as well compare D2's Nightmare difficulty viable builds to D3's TX builds. Just saying.
T13 isn't going to make d3 hard lo. just keep thinking its going to be that hard, and there aren't that many t13 viable builds and maybe you will stop playing and posting here.