Actually we only have 1 weapon more then elementalists do. They get staff/scepter/dagger, we get staff/scepter/GS/sword. Also, thieves have exactly the same amount of weapons we do, but while they have less offhands theirs modify more skills. Sword/Focus or Sword/pistol will have exactly the same 3 first skills for a mesmer, while Sword/Pistol and Sword/dagger for a thief (for exemple) do not.
Personally I think you arent looking at it the right way: its not about the amount of weapons available, as much as it is what you can do with those weapons. The reason why mesmers are very limited is because each weapon is very limited in its uses. Staff only works with a Condition build, for exemple.
This is just another exemple of what I was explaining. Yes, we have as many weapons as other classes, but ours are extremely speciallized. Scepter is a weapon that is only really usefull for Shatter builds. Phantasms stop you from using its auto-attacks, so you cannot focus on them with this weapon, and Confusion is too inconsistent right now to be build-centric. That being said, scepter with a Shatter build does really good.I also found this to be quite annoying. The scepter I have noticed that the last shot (3rd attack the spawns the clone) still overwrites your phantasms. I can have three duelists up from Pistol OH and then bam third scepter shot goes off and one disappears replaced by the clone.