There... is so much math in this post. I think some backstory to the Riskbreaker job itself might help further your cause, from a conceptual standpoint. Because you can skin a melee job any way you want really, but for the Vagrant Story aspect at least, well... There's an overall aesthetic trying to be achieved. I haven't played FF11 but I still occasionally boot up VS, so let me give you the layman's view on that.


In Vagrant Story, Riskbreaker is treated as a specialist job even though it's basically all you get. You get various skills (some from just doing the story and some from dungeoning) that you program to 3 of your controller buttons (I think one button was a cancel). Each successful skill strike adds to your Risk Gauge. Timing is important. Vagrant Story has a pseudo 'Style' system like DMC where successful combos/chains make it so you can use your flashy finishers, called Break Arts. These were different based on the weapon you were equipped with (there was one for bare-handed too, I believe) and also had different buffs/side-effects as well. The better your timing, the faster you could use your Break Arts, but conversely the more risk added to your gauge per strike. Why would this be bad? Well...


Here is how Risk works: the higher your Risk the higher your potential critical severity, but the lower your hit percentage. Like... REALLY LOW. With a full Risk Gauge you can expect 2% or lower for hit percentage but the hits you do land hit much much harder. Thus making Risk management your priority. Generally speaking anything higher than 75% Risk Gauge (maxed at 100) is pretty much unfeasible in a combat sense. Vagrant Story allowed you a full range of spells as well but these were not a part of the combo system, though they also affected your Risk Gauge. (Everything but items did, really).


So the OP is spot on with the Crit aspect of this job. Implementation would be fairly easy. Successful combos would fill your Risk Gauge, letting you use various finishers or Break Arts depending on how high the gauge (each Break Art would deplete the gauge depending on Risk cost). I don't see the Risk system translating over directly (like with the penalties) but it'd work a lot like other jobs with such a gauge (like Warrior and Ninja) so it wouldn't be too much of a learning curve. Break Arts should have various buffs or debuffs and having a full or partial Risk Gauge should like... buff your critical chance with a full one granting a buff to critical damage (but not enough to stay in that state--I'm thinking of doing duties in lower levels where finishers are often not available). Like maybe 1-50 Risk Gauge giving you a Crit chance buff and a 51-100 giving you a Crit damage buff (or however that works here now--it's changed around a bit since I last mucked around with it). There should be a few skills you can spend Risk/MP/TP on that do some magical damage. I'd personally like to see 'Banish' since that spell already exists in FF14 and was an awesome instant-death spell in Vagrant Story.


Sorry I'm not familiar with the Foebreaker class, but WE'VE DONE ALL THE WORK FOR YOU SE--lets do this.