>Can you explain how, for example, a good arial dagger spec is
>weaker than an evil arial dagger spec (on the arena for
>example) or a good elf invoker vs a drow invoker (no cabal
>powers).

A good invoker can't cast area spells in a place with lots of goodie bystanders. A good dagger spec shouldn't just immediately abandon groupmates if they're attacked. A good character can't lie and claim diplomacy then attack when the other comes unprepared. A good character can't choose to kill the easy-pickings of the same alignment, or probably even neutral alignment. It's harder for a good character to get away with not showing up at a cabal defense where they might die.

The ability to attack anyone you want whenever you want gives you the ability to pick easier fights, and the ability to run away from anyone you want whenever you want makes it easier to avoid dieing. Good vs evil doesn't give you a direct mechanical advantage, but it strongly affects the sort of strategic situations you get into.