Yeah Death attack does get much less useful if you are a PC, however the DC is not low. Also, of course you can optimize your saves, in my example the characters have decently high saves. We know we can get really high saving throws, but not all characters do (some dont want to waste the ability increase, feat, level dip, ability point, etc, etc, and they cpould still be optimized (an optimized wizard with low fort. is HIGHLY possible). So, saying "we can optimize saving throws" has little to do with the relative power of death attacks DC. Also, the DC of death attack is dependent on the characters Int. So if you can get high Int. your death attack is higher. Choose a race with a bonus to Int. also funnel all of your ability increases into Int., give Int. an 18, buy the most expensive Headband of Int. you can afford, find feats that increase Int. dependent variables (I am sure there may be one, like spellcasting prodigy but not resticted to spell DC's), cast Fox's Cunning (+2DC an assassins spell!), etc, etc, this character will have a high Death attack DC (and there will be situations where the PC can shine). One can even optimize a NPC 2 levels above the assassin and it could still kill him with death attack (Fortification is good though). Yeah a paladin with high cha. cloaks of resistence, high con., dips in fighter, etc, would be very hard to kill with death attack (yeah for divine grace!); but that doesnt mean a DM could create adventures to that are winnable yet still challenging for the assassin PC (even against higher level optimized opponents). If you read the prerequisites for Ability Focus (monster feat), and if you are allowed to take monster feats, then thats +2 to DC (the prereq. for ability focus is a "special attack" it doesnt seem to restrict that to "natural" special attacks, so death attack may qualify you for ability focus (It is a special attack its just gained through a class).