eh i checked it out, yes, you are correct, it does not tick up with vulnerability, must be done after the vulnerability hits. Though, the difference is small, every bit helps, HOWEVER, I decided to do some tests to see the total dmg and i have to say, I don't agree still... here are my results (i did not upkeep DE for this, for EITHER of my testing)
Your rotation of: TA goes SF MU 1-2-(duality)AE
949 dmg for SF
317 for Mut
796 for SE
1057 for GS
1672 for DAE
1697 for AE
Total dmg for purely the rotation was 6488 dmg
The mut ticks were: 223+152+149+234+152+151+145+142+147+142 = 1637 dmg
The SF ticks were: 204+225+204+323+210+204 = 1370 dmg
Total outcome in dmg for your rotation = 9495
My rotation WITH mut and SF on BEFORE the TA of: TA-2-DAE-1-2-AE
1054 dmg for GS
1684 dmg for AE
1571 dmg for DAE
775 dmg for SE
1079 dmg for GS
1680 dmg for AE
Total dmg for purely rotation = 7843
The mut ticks were: 141+139+141+154+144+149+151+148+147+139 = 1453
The SF ticks were: 203+190+199+203+203+199 = 1197
Total outcome in dmg for my rotation = 10493
This was only 1 round of testing. But in it, I will say, your DAE produced higher than mine did. Non of these were crit hits above.
I never said do not use SF and MUT. I said apply beforehand and use the vulnerability to maximize your attack dmg in single hits (AE). Not to mention, you give yourself TWO opportunities to get a crit AE in here, which alone would be well worth the extra dmg. The chances of you getting a crit tick of SF or MUT every tick are extremely thin. And without it, it won't add up to the boost of a critical AE.
As for that last part about the healing with mug. 2000 seems negligible too when you compare it to your total hp. But it can be the difference between you standing and you on the floor. I'm not saying it'll change your life, i'm saying every bit counts, just as you are by saying use SF and Mut to get the dmg tick buff from the vuln. And more so, it's better to be careful NOT to overuse stun. VA comes to my mind quite often as I can't tell you how many times howl's have gone off because we have too many DPS spamming their stuns away for that bit of extra dmg and then we all get massive dmg because I can't stun when I need to.