From what I know, critical hits pierce through defense buffs and lowered attack stats.
For attack buffs and defense drops, Critical hits do not pierce through them.
The reason you lost to Pimpnubz while u got a crit is not because the critical hit did not "pierce" your lowered attack stat, but rather the fact that Critical hits are nerfed from double the damage in gen 1-5 to only 1.5 times the damage in gen 6.