Not saying it isn't frustrating, but the SAM has a requirement which is that the target you want to kill hits you with Hissatsu:Chiten, which is on 30s and last 5s, and that you use the LB during the 3s they're affected by Kuzushi.
I don't know if Kuzushi triggers from AoE dmg.
I don't mind the OS because there are some condition that must be met, but the 24k baseline on a straightline is a bit too much "on top of the OS". At least it's 2min CD.
I play MCH so I'm obviously biased here but I really don't mind the 3% OS even when it affects me because it is not free. You need to spend one of your precious Analysis charge and that 3% OS is the ONLY benefit you get from it. No more dmg nothing. Just that. So everytime I use it, I take a chance, "maybe". I personally only attempt it when people are pack and I can hit 4-5 people or if I'm about to die (might as well). But during regular fight this can actually be pretty costy if people are spread. Using it there means it's not up for the next Drill, so 9000k lost. There's a risk reward factor that people not playing the job don't seem to consider. I've went through tons of match with over 30 hits with boosted chainsaw without landing a single OS, so loads of wasted Analysis.
It is not a free kill button. You have 97% chance to waste your 15s cd (which is the basis of your entire gameplay).
Also people only often only consider when they're full health, but it can also triggers when you're low, which reduces its value greatly. when you shoot a Drill on 5 people and the one that get OS is the one that was already nearly dead, it really feels like "unlucky luck". Personally when my team is winning I never boost it. I'm already winning, I'd reather secure kills with 100% effective method like, dmg, slow and stun. However it feels totally appropriate when your team is dead and you're running for your life with 5 people chasing you. My best (happened only once) was a double OS when the whole team was chasing me as the last survivor. That made them stop chasing me... We still loose tho. Ah and final reminder, I can't spam the Chainsaw... there's a 40s CD on that skill because you need to cycle through your things. 3% on a 40s skill that requires another CD... just try for real... I've had a few of my friends who complained actually try. Most never landed a single OS for the simple reason that... well it's unlikely.
NIN should perhaps have a limit to its reset count, like once or twice. 50% is also quite high. Many attacks can drop someone below 50% in a pinch. so perhaps 35% or 40% would feel more adequat. But let's also not forget that it does 0 if the target isn't below 50%. Feels bad to LB someone at 50.1%.
In summary:
Personally I find the SAM to be the most annoying, not because of the OS especially but more because it also deals that 24k slash in a line. Seems a bit too brutal.
I think MCH is fine because there's a very high risk. When the reward triggers, obviously it's great (or it sucks) but I wouldn't be surprised that the meta would be more about skipping that unless you're loosing (so you might as well give it a shot)
NIN's does a bit too much for it opportunity cost. 50% isn't that low, there's no limit to the reset and you still have a 5s window if you fail your OS. Its CD is also only 90s.