Lifesteal is just so your damage dealer can survive longer, so the substitute is anything that can make your damage dealer survive as long as possible.

Lifesteal have limited effects against strong enemies with buffs/shield/defend buff. Continuous Heal buff may work better.

First it's 4 gears set - gain 30% lifesteal instead of increase attack/speed/defend. 

Second, attack opponent with shield gain 0 life, especially when attack champs with divine gears. 

Third, you are slower, got attacked before you could attack.  

Fourth, you are weaker, got beat harder. 

Lifesteal should be mainly used for farming/campaign, when you only use 1 champ with no heal buff. 

Once you get to 12-3, you want your farmer to not need any healing at all, your farmer should be able to go in and hit everything dead and finish the level in 30 sec or less, and lifesteal set hinders that

Here's my Athel that is built specifically for farming 12-3

https://i.imgur.com/ipKVLml.jpg

There are others who build their farmers so they can farm 12-3 under 15 sec, for me 30 seconds is good enough. And the gears needed are not that crazy high

ClosedPoly said:

It seems like every dungeon and the CB require lifesteal as recommeneded gear.  I have the gear but I cant get the substats that I need out of it.  Would Defense and Resist work as well?  Or just break up sets and forget about the Lifesteal bonus? 

Is there a healer that I can use in place of lifesteal?  An aura? 

For CB, the goal is basically to keep surviving as many rounds as possible - unless you run an unkillable composition in the endgame, sooner or later the CB will start one-shotting your team even while he's debuffed and your team is buffed, but until then you don't want anybody to die from being low on health. It would take a pretty crazy healer to keep the whole team on full health if they have to do it all by themselves - and anyway you'd prefer not to lose a slot on a champion who's only healing (personally I've got Sethallia who does HP burns as well as healing, so it's a little different). 

That being said, for most champions lifesteal won't help you very much on the CB until you get warmaster/giantslayer, because until then they just don't do enough damage to keep healing themselves up. So if you don't have your CB team at level 60 yet, or you just don't have a viable CB team at all yet and are just getting by with temporary champions, then indeed lifesteal gear for CB isn't that important yet - though you may already want to work on farming it. 

For dungeons, lifesteal will really only make the difference for champions who do a ton of damage on AOE - and in some dungeons, there is no AOE anymore in the final stage. For single target hitters, it could help some but it probably won't be enough and you'd need a healer anyway. 

who said lifesteal can't make it under 30 seconds ? Actually when my Kael/Athel/Elhain reach lvl 60 and 6 stars, with any lvl 16 gears, they could farm Brutal Campaign Naturally. And yes, I do use each of Kael/Athel/Elhain to farm brutal campaign for at least 2 months each.  

If you can do 30 sec on 12-3 then no healing is necessary, it's redundant... Then you can use lower star equipment that add more stats.

Also you have the flexibility on looking on the main stats / sub stats rather than using the 4 slot lifesteal set. Rather inefficient I have to say, using lifesteal for farming 12-3

Even my Athel is kinda too much for  30 sec run on 12-3, but since she was my first 6* I use her everywhere. Now that I have more heroes, I stopped upgrading her equipment, and allocate the resources elsewhere

That being said, I do use lifesteal on Kael, but he's restricted to CB, as my 2nd poisoner.

His damage (outside of the poison damage) justify for him using the set.

Unlike Occult Brawler whom I just slap accuracy and HP%

rh15 said:

Do you have a healer to go along with occult brawler? Or does the a2 do enough to keep him alive. I have a life steal set on him but wondering if I should get the extra defense or accuracy. 

For CB? I straight up put highest accuracy I can, HP% then Def%

I also have Doompriest as healer in CB also cleaning up Occult Brawler's self poisoning

rh15 said:

Do you have a healer to go along with occult brawler? Or does the a2 do enough to keep him alive. I have a life steal set on him but wondering if I should get the extra defense or accuracy. 

For CB? I straight up put highest accuracy I can, HP% then Def%

I also have Doompriest as healer in CB also cleaning up Occult Brawler's self poisoning

I don't know about you, but personally I don't think his hit damage is worth equipping life steal set