Well..
Ninja is a very hard to play class.. It forces you to be sneaky and THINK about what you are doing. The mind is the armor.. We are self nerfers basically.
Overall player skill has increased so you don't get so far with a spammy katana anymore. Archers are AGI based, which means you cannot catch them without 8 Athletics. Archers are BETTER(!) than they used to be. Besides they are incredibly more aware than they used to be. Also there are more cav, and that makes them look around them all the time. Before I could usually catch an archer and kill him while running uphill and dodging.. Either my dodging skills have gone stale, or they are simply better at reading it.
Still it's not that hard. Bring a short sword and a bamboo spear, go flank. Try not to get seen. use hills, bushes and trees for cover and you will backstab those archers in no time. But do not expect to be a 2h hero in the middle of battle. For that you need a greatsword, different skillset and loomed armor.