In a Mesmer funk.
1. In terms of min-maxing, there is always a “best” if you can define the situation narrowly enough.
2. Focus+trait can “break” certain fights in PvE. Other than those situations, it’s not 100% mandatory or anything.
3. In WvW, there are many segments of gameplay. Due to the nature of WvW, many or most of those different segments synergize very well with Focus. There are some WvW aspects where it may be similarly effective to choose another weapon, but those are few and far between.
I wouldn’t even mind having the focus on a second weapon set to go with my Sword/Pistol or Sword/Sword. The problem with that is I am stuck with the Scepter, and I have a hard time justifying using the Scepter when just using a GS or a Staff seems infinitely better.
I recently switched my build to have a traited Focus (the CDR/Reflect as well as Phantasmal Haste for Warden), but in terms of PvE content, I liked having 3 Phantasms up at once doing damage, and I feel this is not feasible with Warden. I also probably just need more practice and experience with using Warden, as I am not entirely sure how his reflect works, how his spawning works, and under what situations he will move. But I find myself dropping him, and if he’s lucky, he gets off one whirling combo before the enemy moves out of his range, unless I stand there and tank it for him. After they move, I just detonate him with the other clones I might have up. I guess this would put me in more of a support-y role than damage role compared to stacking bleeds and damage with Duelists? It might just be I need to go to a lower level zone and practice utilizing my Warden as well as the wall (and how the dislocation on it works; it always seems to throw them forever away).