Ah "The build" , the most annoying thing in most rpg.
It reminds me of when i first played Neverwinter Nights, my goal was to run something like a ninja, basically a "hide then stealth kill" type of character.
While NWN does not have a ninja class, it had Rogue then the Assassin prestige class when meeting the requirement as Rogue felt ninja enough to me.
Rogue then Assassin sounded the most logical to me, but at the time i never looked into "The Build" to have an actual working assassin for the game setting, because an Assassin built from Rogue then Assassin lead to your special death attack bein useless against anything that is considered a boss or an undead (they're nearly all immune to the paralysis effect ), the backstab is useless against half of the game enemies (they're all variant of undeads anyways all immune to backstab too) , the poison, well it's not going to win you any fight against anything that is not low level (and undead do not care anyways)
At least the sneaking worked to avoid being seen, unless you encountered a scripted enemy that automatically knows you're there, and ghosting whole maps gave you no xp, so you were going to be underleveled after a while against those scripted enemies, without mentionning that past mid-game every enemies have some way of using a true seeing effect, allowing them to see anything hiding