Updated T13 priority (2p+):
1 ST_0 Searing Totem with 0 ticks remaining 2 SS Stormstrike 3 LL Lava Lash 4 MW5_LB Maelstrom Weapon x5 stacks + Lightning Bolt (4.5) (MW4_LB_SW) (Maelstrom Weapon x4 stacks + LB (w/Spirit Wolves up w/4 piece)) 5 FS_UEF Flame Shock if the Unleash Flame buff is present 6 UE Unleashed Elements 7 ES Earth Shock 8 SW Spirit Wolves (on boss) 9 LS Lightning Shield if expired 10 ST Searing Totem (with x ticks remaining) 11 MW2_LB Maelstrom Weapon x2/x3/x4 stacks + Lightning Bolt
As an aside, I saw LB go from 9.5% or so of my total damage done to 11.5-12% when I got 2 piece. On our first H-Ultraxion kill (as close to a pure burn, tank-n-spank fight as there is), I fired off as many more LBs than SSs as I did SSs than LLs (which is to say I had 45 LBs, 38 SSs and 30 LLs). The 30 LLs did more total damage than the other two, but the total damage done by SS and LB were fairly competitive...part of the LL being so much higher is almost certainly because I'm wearing 2p/2p instead of 4p, so that may change. Since LL was lower priority I averaged an extra global past the cooldown before hitting it, but I was well within reaction/lag time on SS. I got an LB on average of about every 7.5s (or 5 globals) meaning that my "cooldown" on LB was less than SS...which suggest that you might benefit from putting MW5_LB (and MW4_LB_SW) above SS and LL, but sims say otherwise. I haven't done any in-game testing of my own, so I'm leaving it as it simmed out.