First, it's refreshing to see that when hot issue such as this rears it's head, the dev-team has the resources to focus and respond.
Second, it is a step in the right direction, although as presented it requires a reduction in both the amount of the penalty and the duration of the debuff.
Third, there is an issue that needs to be addressed: the myth that most PM's or necro-focused AM's can sweep through epic content and lay low virtually all of the content, with little challenge. This is simply not true, and really only applies to the top percentile of necro-focused arcanes.
Quite frankly, if a player has invested enough lives into an arcane to have +9 spell pen (3 x wizard and 3 x favoured soul past lives), the maximum possible intelligence (i.e. completionist) and farmed out the best possible gear (+4 intelligence tome, tier 3 alchemicals...) then they had better be dominating content, for two reasons.
First, it is consistent with the lore that comprises the foundation of the game - that at the highest levels, spell casters are indeed the most powerful.
Second, if there is no tangible benefit to investing countless hours TR'ing and raiding and farming gear, then where is the underlying motivation to continue?