It is a bit easy, but that's why there's so many enemies you have to fight off at once.
Assasins Creed isn't about the combat, that's the point. Usually when there's combat it means that you've either messed up the stealth or you have to run away and chase someone while the enemies that are trying to fight you are just a distraction. The assasination mechanic is easy enough to do as long as you don't get seen. But yeah, the amount of enemies there are to fight off when there is supposed to be combat is to make it harder as there's so many things to keep an eye on. Like the ship combat is a bit more harder as you have to steer, aim and fire all at once, for me I find that type of combat is more fun.
This is just comming from me playing AC1 and 3 and a bit of 4 so if anything about the combat changed in the later games I'm sorry I missed it out.