Disagree with insight, aside from my first 99 lock (who used insight weapon) - I haven't needed insight on an ES or BB lock on their journeys to 99. Siphon and a little mana leech is all that was needed to keep the blue bulb full. Occasional use of a mana pot if in an area with tons of skeletons like stony tomb or something, but even then, there were usually enough zombies to leech from.
Lumping ubers in with heralds and baal seems disingenuous (unless I'm misunderstanding your point), as ubers aren't part of a regular whole game clear (unless you get amazingly lucky with statues I suppose) - it would be every third game at the absolute luckiest, if you get a key from each boss on each game (unless you get triple key drops 3 times...then I guess you can do it in 1 game).
Furthermore, while ubers with BB is possible, and kind of fun using their summons against them, echoing makes easy work of them very quickly. Uber ancients with BB is brutal...would be faster to grush up a new ES warlock and take them down with the new char once you put on some basic equipment lol. In both cases, BB and ES, nothing more is needed for safety than the usual pre-buff and swap out some mf pieces for res/absorb gear (ie nagel for ravenfrost).
If you factor in all these other expanded content, then echoing is much better and faster, but again, if you're just clearing certain high density, low hp areas, BB has the edge.
But most importantly, at the end of the day, both are good builds! Still might want an echo lock or smiter for ubers/ancients though lol
Last line of the guide: "Uber Ancients: Get an ES lock to do it for you"
It's just so rough trying to single target one and not others. Just a terribly inefficient and ineffective fight for a BB lock, and not worth doing. Just wear full Horazon's and an obsession with a lvl 80 ES lock and do it safely, might level up another one just to get back to doing stuff like that.
I don't think p8 Baal is that big of a deal. It takes longer, but it's not awful and I've never felt any risk as BB in doing it. I boil until the demon is at 25% health, let him/the merc attack while the demon regens, then repeat a couple of times and he's dead. I think infinity on the merc very much helps in that fight.