Leech together with Warmaster/Giantslayer is the best way to keep your team alive in non-unkillable teams. To achieve that, you can use lifesteal gear or leech debuff.

If you use him for CB, you don't have to bother to much about attack and crit rate. His damage comes from Warmaster on the A1 or the Giantslayer-like effect of the reflected damage.

To be honest, Lifesteal does not do much for him anymore now it no longer procs his passive.

But it doesnt hurt either ofcourse.

I still run mine with lifesteal (Mainly beacuse I am lazy)  in an killable setup that easily 2 keys ultra nightmare. But to be honest, if I give my team a little bit more love, that might just be a 1 key.

Most important thing to remember: He gets his damage from his passive. That means he needs accuracy to land that HP Burn. After that, its just a matter of keeping him alive. Everything else is bonus.

stalwart

a man of many words, Trips is. likely the correct answer here. 

also stalwart is extremely underrated. 

Of course, Stalwart or other sets runs under the assumption that your CB team has someone with Leech. If you don't have that, then all five champs *must* run Lifesteal. Trying to run a CB team without either is a recipe for disaster.

not necessarily.  an unconventional comp with zelotah for example will provide sufficient shield/healing until round 40ish when the lifesteal/leech is insufficent anyways.  Leech is obviously still recommended, but for "beginner" comps u work with what you have.  And my recommendation for stalwart is only with good stats.  Stats still more important than a crappy stalwart set.