Looking at diversity, particularly from PvE, we have a lack of weapons diversity. I will focus on guardian as an example, but this thread is not about one specific class (and I will use other examples). I also want to add, this is not about top efficiency, but realistic viability.
Starting with guardian, and primarily in PvE, all power builds are concentrated around great sword and scepter. There is not really much room for any improvisations. Sword can be okaish, but the difference between it and sword and scepter or great sword is large, especially in a group setting. Hammer is even worse. Hammer offers protection, but no one uses hammer for that purpose (even in PvP). Even if you consider protection into the mix saying that great sword out classes hammer in PvE is understatement of the year. On the other side, scepter is jammed into every single damage based PvE build, due to one skill. Long bow is also out classed by an insane margin by scepter. In addition, great sword has a leap, CC and a pull. Compared to other options, it actually has the highest utility. And just to be clear, I am not talking about 5-10% damage margins, but margins that are much larger (35-40%, if not even more). Even in open world PvE, unless you deeply into RP, you hamper yourself significantly veering off the meta weapons.
Warrior, kind of the same. Great sword is a must in every single power based build (even PvP builds). Mace is not used in any game mode. Dagger is only used as a utility weapon as MH in PvP, but nothing more. I kept convincing myself that daggers are really cool, and used it in PvE over great sword, but in the end I gave up. The difference in damage is astronomical. I tried to use hammer in PvE and it failed miserably. Mesmer, actually is probably the only class I can think of that every weapon is good in PvE in at least one build, except scepter, which is terrible in every game mode, even though it has not utility what so ever. Rev, staff in PvE. Short bow in PvP. Ele, MH dagger in every game mode. Scepter in PvE (it is not great in PvP either).
I think these are enough examples.
To have specific questions:
Appreciate input provide