First of all, Sniper sucks to begin with. Who cares about growths and such. Its about the battles. They lack of melee which hurts their overall performance.
Secondly, Assassin's are considered one of the worst class amongst most experience players, alongside with say Snipers. They happen to have the worst Str cap of 20 which is quite not good when you think about it. They're also complete reliant on the RNG, even more so than most other classes such as Beserkers and Swordmasters for instance. They depend on the RNG to put out critical hits. Especially their skills, Silencer which happen to be no better than critical hit in a LOT of situations. Meaning they need to relay on killer weapons such as Killing Edge or Shamshir in order to active their Silencer skills to be of decent use. By doing so, it would probably result losing many of your funds. They also lack of ranged weaponry since they're usually weaker than physical weapons of the same level, which hurt their cause even more.