Glass Cannon is just an absurd talent. 2x AP will result in dealing much more than twice the damage/turn, since you typically can't use all your AP on attacking, but will lose a bunch of them for (de)buffing, moving or healing. This also means that the buffs will be applied to more attacks before you have to cast them again. With GC you will also be able to use more expensive abilities without waiting. Furthermore Mages can cast elemental combos the same turn (like Boulder Dash + Fireball) and get another chance if their target saves against a immobilizing status effect.
-50% HP doesn't mean losing half your HP, as stupid as that might sound.
The -50% penalty is added to all the other modifiers you might have, which are Picture of Health, Lone Wolf and the difficulty modifier. The difficulty modifier is +60% on easy, +15% on normal and -25% on hard.
So without other talents, Glass Cannon would change the HP like this
easy no PoH, no LW: 160 -> 110 = -31%
easy PoH 2, no LW: 170 -> 120 = -29%
easy PoH 3, no LW: 175 -> 125 = -29%
easy PoH 4, no LW: 180 -> 130 = -28%
easy PoH 5, no LW: 185 -> 135 = -27%
easy no PoH, LW: 230 -> 180 = -22%
easy PoH 2, LW: 240 -> 190 = -21%
easy PoH 3, LW: 245 -> 195 = -20%
easy PoH 4, LW: 250 -> 200 = -20%
easy PoH 5, LW: 255 -> 205 = -20%
normal no PoH, no LW: 115 -> 65 = -43%
normal PoH 2, no LW: 125 -> 75 = -40%
normal PoH 3, no LW: 130 -> 80 = -38%
normal PoH 4, no LW: 135 -> 85 = -37%
normal PoH 5, no LW: 140 -> 90 = -36%
normal no PoH, LW: 185 -> 135 = -27%
normal PoH 2, LW: 195 -> 145 = -26%
normal PoH 3, LW: 200 -> 150 = -25%
normal PoH 4, LW: 205 -> 155 = -24%
normal PoH 5, LW: 210 -> 160 = -24%
hard no PoH, no LW: 75 -> 25 = -67%
hard PoH 2, no LW: 85 -> 35 = -59%
hard PoH 3, no LW: 90 -> 40 = -56%
hard PoH 4, no LW: 95 -> 45 = -53%
hard PoH 5, no LW: 100 -> 50 = -50%
hard no PoH, LW: 145 -> 95 = -34%
hard PoH 2, LW: 155 -> 105 = -32%
hard PoH 3, LW: 160 -> 110 = -31%
hard PoH 4, LW: 165 -> 115 = -30%
hard PoH 5, LW: 170 -> 120 = -29%
Glass Cannon is so good that you should not pick a talent at level 3 so that you can immediately use it when you get to level 5.
Lone Wolf is a talent that you should pick at level 1 or not at all, since otherwise you will be missing out on ability points.
Lone Wolf is interesting for players that are playing on hard difficulty, because of the HP and chance to hit penalty. If you are not playing on hard difficulty, Lone Wolf will significantly weaken your party.
