Zanshin? why?

[Jacs]

You shouldn't really dismiss Ikishoten so easily without at least considering the math. Assuming you use a 450 delay Great Katana and have the gear for a true 5-hit (74 Store TP in merits + gear), an Ikishoten (level 4) hit would give you 40.8 TP [(11.5 + 12)*1.74]. Thus a miss + Zanshin proc and land is in effect worth a little more than 2 regular hits landing. In essence, a landed Ikishoten hit shaves a hit off your build.

Note: I'm neglecting Double Attack for simplicity. Zanshin can't proc on a double or triple attack, so its value is diminished the more of those you have.

If you are talking about a single swing, a landed Zanshin hit will occur about 2.1% of all swings (0.05*0.45*0.95). You can look at it slightly differently though by considering build cycles to 100TP. If you are at accuracy cap for all melee swings and weaponskills, there is a 77.3% chance of landing your WS and 4-hits in a row (0.95^5). There is a 3.9% chance of missing a weaponskill then landing 5 hits in a row (0.05*0.95^5). Thus on 81.2% of all your TP build cycles, you won't have a chance for Zanshin to activate. That means on 18.8% of your TP build cycles, you will have at least one miss of a normal melee swing. 45% of those misses will trigger a Zanshin attack. It ends up having more impact than you might suspect just by considering a 95% accuracy rate. It is somewhere around ~6% of all TP builds to 100TP will see it be "useful" (meaning ignoring build cycles which put you at 120TP).

I personally used to have Blade Bash 4/5 and I did really like it. It was great for small group activities like Nyzul where a stun could stop a painful AOE. I have since switched it out for Ikishoten 4/5. I think the choice comes down to what you do with your SAM. I personally use mine for pure damage. SAM is my "main", but I am on other jobs more than I am on SAM. If I am to tank for a larger group, I will generally be MNK. If I am low manning, I will be NIN or THF. If my LS asks me to bring SAM (which they usually want MNK ;; ), they only want me spamming Fudo's. I just found myself rarely needing Blade Bash anymore so I rolled it back for Ikishoten. Neither is particularly game breaking.

All that said, I agree the set bonus on SAM AF3 sucks. Personally I would have rather seen something like Zanshin being able to proc on a normal landed melee swing, effectively being like double attacking I guess, but it would work with Ikishoten nicely.