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).

Evils have some exclusive classes like necros/ap/orcs but goodies have paladins. Also, more goodies are more often backed up by healiers and have sanc (healers/paladins).

It more restrictions, set of enemies, and average player skill among alignments that matter, not the actual PK power of a character.
For example, people in Fort have only two opposite cabals while Empire gets more action.

Just quick stats from top pkillers by align

evils vs good:
Kostyan 174
Djabree 95
Kharghurln 183

goodies vs evil:
Niheriva 150
Alriac 119
Gryshilniar 110

I dont't see a significat swing here considering that two of three evils here were emperors with sick powers and hours.