Weapon sets based on Lethal damage aren't useless. You just have to pick and choose your foes a little to avoid the ones you notice resisting the most (such as Malta Titans). Most of the time, though, you're not really going to notice that you're killing things a bit slower than others of the same archetype. Unless you're the obsessive type, anyways, and start tracking your stats on different characters of the same AT with HeroStats or some such thing.
Other than Malta Titans, really, there isn't much that resists heavily enough *and* is dangerous enough that the slowdown'll increase your faceplant odds very much.
Lethal Damage is the most commonly resisted form of damage in the game. More things resist Lethal Damage than even Smashing Damage.
Most Commonly Resisted Damage is not synonymous with "useless" though. All it means is that the min-max crowd will turn their nose up at it, because some other damage type is resisted by 2% fewer hostiles (statistically speaking).
If you want useless, try Negative Energy against CoT Ghouls and Ghosts ... and even then, you're still doing damage to them.
So long as your damage output is greater than your target's regeneration (or heal) capabilities, your damage is not "useless" ...
It's the end. But the moment has been prepared for ...
Rikti Soldier bosses are one of the only things I ever notice that slows down my lvl 50 Broadsword Scrapper. Otherwise he just plows through most things pretty quickly. With AS and Build Up, Ninja Blade shouldn't be much different.
I've noticed other things that do this too before but they aren't common enough that I remember what they were. Or they were things like Malta OpEng Gun Drones but those aren't dangerous at all, just an annoyance that takes longer to get rid of.
Towards your trek to 50 you will encounter mobs that resist psychic damage more than lethal. There are mobs that are very vulnerable to lethal (e.g Carnies) damage too.
NB, DB, BS, and Spines are all more than satisfactory. Claws is the set that has given other lethal sets a bad reputation in my opinion.
How good is Ninja Blade now?
Well, between Ninja and Broadsword, I would take Ninja because Ninja is much faster. I wish they could distinguish these two sets more besides just activation/damage ratio.
"Useless" is very harsh. There are some bosses that will take you 50% or longer to kill like Ritki bosses and Crey Tanker Boss.
I guess that's why Ninja Blade can take chance to reduce resistance proc. It helps eventually.
What's left is to normalize all Assassin Strikes and improve Stalker's old sets (Claw, MA and EM)! You don't need to bring back the missing PbAoE attack. You just need to make the existing ones better! For example, make Slice a WIDER and LONGER cone.
So i want to make a Nin/Nin Stalker and level it on and off with my claws/regen stalker, but from what i've heard, any type of weapon set is useless in endgame because of the higher lethal resistance. So question is, how good is Ninja Blade right now?