Okay, I give up. Fencer wins. I swear I used it to force a 100% crit rate in the past, but I can't for the life of me get it to happen now. The reported critical hit rate boost is 5%.
Control: DNC/WAR, Joyeuse/OA2-4 Parazonium+2 with Dark Depths/Gnarled Horn/Razed Ruins - ~2000 hits and 95.3% Critical Hit Rate
Test 1: DNC/WAR, OA2-4 Parazonium +2 with Airy Buckler and the above Atma - 1505 hits and 95.55% Critical Hit Rate
Tests 2-5ish: Because it was predicted that this would cap my Critical Hit Rate, I swapped some things around while leaving the parser running to see if I could affect my average at all/make a case where I don't non-crit. I tried:
* Martial Knife, remove all DA/TA gear - Plenty of non-crits, N=300 and the average didn't move
* Parazonium +2, use TP every time I hit 100 - Plenty of non-crits, TP usage didn't seem to matter.
* Remove/add various gear that might have a hidden effect: Lowers Critical Hit rate - I cycled through about all of my gear (all of which I was wearing in the control test) and nothing mattered.
Abyssea Altepa, this time on WAR/DNC:
* Fencer IV, no AF3+2 pants, Joyeuse, Rancor/Zahak's/AF3+2 head: 316 crits without a single non-crit (.99^300 < .05, so we can be 95% confident that it's 100%, I think)
* Fencer IV, no AF3+2 pants, Joyeuse, Zahak's: 826 hits, 812 crits = 98.3 +/- 0.88%
And yeah, I confirmed that I was getting the TP Bonus from Fencer in both cases. On WAR with Spirit's Within, and on Dancer by using Aeolian Edge at 180 and 200 TP on the same mob with Martial Knife.
The options, as I see them:
1) Some technicality is preventing me from getting the crit rate boost (like having access to DW even if I'm not doing it).
2) Fencer crit rate boost is a second shot at criting if you fail the first time with its own (low) crit rate. So say you have a 20% crit rate normally (BST WAR pet). A 6 or a 7% second-shot proc rate would result in an apparent +5% crit rate. If you have a 95% crit rate though, it would only add .3% crit rate.
3) You don't get the critical hit rate bonus when wearing a shield, though you do still get the TP Bonus. This one wouldn't make sense to me, but I guess it's an option.