If, theoretically, there was a mod that made it so that taking Glass Cannon reduced your base Recovery AP prior to the GC buff being applied, how much of a reduction would be necessary for it to be balanced?
Like if the reduction were 3.5, then with 5 speed + GC would equal (3.5 base + 5 speed - 3.5 GC penalty)*2=10, while without GC and 5 speed it would be 8.5, with the difference increasing by 1 with each point in Speed. At 10 speed it would be 20 vs 13.5 for example.
Or would it be more balanced if GC were to multiply AP recovery by a smaller amount, like 1.5x instead of 2x?
I think another interesting interesting way to nerf GC would be to add more disadvantages to it. Maybe a reduction of some sort to BB/WP, resistance, armor, greater reduction of vitality or a combination thereof. Make the glass cannon health reduction harder to counter that is. That doesn't solve the problem of high AP + high initiative + Control spells stopping any foe from acting at all though.
Maybe just add a flat -2 or -3 speed modifier to force the player to invest more in speed and thus have less points to add to constitution.