AskMrRobot, while being a fairly nice site, is sometimes inaccurate. They aren't as up to date on the changing information. It's nice to use as a kind of guide, but I wouldn't rely on it 100%. The ElitistJerks forum for Rets and the longer threads here about t15 and t16 stuff will keep you more up to date about the changes. Sometimes just progressing through the tier and getting more gear will change how you gem, enchant and even your rotation. We've seen this this tier with the CS>J>Exo changes and the Expertise/Haste gems giving you a net gain in Mastery. This is why many top-end Rets will advise people to sim their characters for the answers.
As for Execution Sentence: You like to wait for trinket procs, mainly, because it takes a snapshot of your stats when you cast it. So, even if you have 130k AP for 1 sec.. if you get the ES off, you will keep up a 130k AP ES for the whole duration of the spell. Means a big boost to that final burst. Another little thing to note here is that your 2pc-T15 bonus will *fluidly* buff your ES. Meaning you would like to keep up that buff on yourself at least for the latter parts of the spell.. if not the whole thing. The extra 6% Holy damage on a buffed ES is nice. This is fluid because it's a debuff on the mob you're attacking and not a buff to you.
*** Synapse Springs (Engineering) can be macro'd into your ES cast (/use10;/cast Execution Sentence) to give you a buffed ES every time. You can see some pretty high numbers on ES if you line it up well with procs.
Revvo has another thread in this forum dealing with Weak Auras. If you don't use this addon it's pretty nice for tracking and making alerts to things like trinket procs, stacks and inquisition timers, etc. Helped me a lot with ES casts and maximizing DPS.
As for weapons, I know your pain. Took us forever to get our first heroic 2-hander. We went like 6 weeks with doing at least 8/13 bosses on Heroic without a 2-hander dropping. In the last 2 weeks I've gotten 3 heroic 2-handers and 1 was TF. So, your time will come.
The .32% is pretty low chance, but if you figure how many times you melee and special attack in a single fight.. it means you can miss quite a few over that span. It's not a game breaker, but it'll definitely help. I hate missing a HP generator. Frustrating.