To be quite honest, 1.5-1.6 PCHP sounds like a bit of an overestimate for Magic Burst. DQ8 damage averages are a bit of a mess, and while I'm open to not holding Dragon Soul or Gigagash against Jessica, I'm certainly going to hold Magic Burst itself against her. Take the following 3-turn average:
Jessica: 384 (Kafrizzle x2, Magic Burst)
Guv: 176 (Gigaslash)
Yangus: 169 (Big Banga x2, Stainless Steel Sickle)
Angelo: 140 (Kaswoosh)
Average: 217
Kill point: 543
This puts Magic Burst at about 1.37 PCHP, which feels a bit more reasonable.
One could also allow weapon switching (I don't), which raises the damage done by Jessica and makes the average 228.
EDIT: While I'm at it, on the subject of Dragon Soul, here's the Level 65 averages!
Jessica: 649 (Twin Dragon Lash 466 x2, Magic Burst 1016)
Guv: 413 (Dragon Soul)
Yangus: 350 (Big Banga)
Angelo: 195 (Pearly Gates)
Average: 402
Kill point: 1005
That's whip Magic Burst for the record since TDL has gained so much damage. Maxed Magic Burst now does 1228, and hence is only 1.22 PCHP. Feel free to point and laugh at Dragon Soul, which is barely above average and misses the 2HKO even if you remove Magic Burst from the average!
EDIT yet again: the above figures assume you are holding the Level 65 PCs against the same average defence as the level 40 PCs. If you don't, the figure for TDL drops. If you're curious, the -max- the average would drop by is to 386 (with Kafrizzle and a staff in place of TDL and a whip), and hence the kill point to 954, which isn't a huge change.