The Pale master should stand as a special prestige type tree... similar to arcane archer with prereqs required to take. They should eliminate most all stat and focus buffs from the tree line and concentrate on making the undead character lines stand out for their special abilities (like regeneration, damage reduction, poison and disease resistance, fear invocation....).
Then stat bonuses and focus bonuses (i.e. necro focus) can be drawn from archmage line or other lines like say fighter line. Prerequisites could include ability to cast 1st level necro spells. This is more Dungeons and Dragons like. In this way, your undead form stands appart and special from your wizard, or sorcerer, or monk, or cleric lines.