I think the skill debuff will mean better results for PvP for guardians and their groupmates. Casters will loose effectiveness because of this and when was the last time a caster had no power for you? This will mean they will effectively be casting those spells at a lower lvl and therefore a better chance to reduce or resist those spells. The skill debuff means we will be mitigating their spell damage while it applies, which is better than saying you can cast one fewer of that spell if you should go oom. This is a right across aboard debuff of any spell effects done while in effect.