This is something that I've talked about before in other posts but I'd like to make a more solid discussion about the 9 professions and how it can be a struggle for new players to get into guild wars due to the expected roles being absent on those classes. Although i don't entirely blame Arena net for this, as the player base did act in an unpredictable way with HoT when arena net started to try and standardize things for the game so Tank and Healers could be a real thing in the game rather than different forms of support DPS and DPS. But the issues of Arena net's system as it is now it makes this problem rather difficult to solve.
New players when they enter into Guild wars 2 are going to have specific expectations from the classes that are presented without ever looking at this skills. Just looking at what they are and how they're described. For instance, Guardian has probably the biggest disconnect for new players and what it actually does and what its role is. What new players expect is a Tank that supports allies and possibly heals to a minor extent. And the way the game mechanics are set up the Guardian is just not really a good tank. They can play the healer/support role fine but they're primarily a DPS, and one of the best at that. I've heard storied of players joining the game to try out a Warrior or guardian to be a tank only to find out that Mesmer was the tank in almost all content which quickly turned them off. Although a novel concept for sure, because the game has such a drastic disconnect from genre expectations this is more likely to turn new players away than to keep them playing.
Human psychology is weird. Humans both want something different but not so different that it breaks with conventions that they would otherwise expect. And we're all like that in some way. It would be nice if most humans could just take on a new experience and just slip into it and be delighted with its uniqueness. And there are definitely people who can do that, but its absolutely not something you should rely on. Its nice if you have that strange option like a mesmer tank, but you should still have those other options, such as Guardian and Warrior tanks, be just as good at that job if not better.
This issue is a bit more complex than all the issues I'm going to bring up but the suggested solution I have would be to change the Aggro system from a "Who has the biggest toughness" to a threat system where all skill either generate threat or reduce your threat so the player with the highest threat level takes aggro. And to keep toughness viable have bosses and specific enemies aggroed on the threatened Ally deal greatly increased damage so toughness gear becomes a necessity. This way if you want to run a support like a chronomancer you could have their supportive skills generate very little threat making it very difficult for them to tank over something else.
Other issues we see are builds that are just not great in pve that have no right not to be at least viable. Minion Master Necromancer and Turret engineer both come to mind as these builds are extremely popular with new players but once they get into more difficult content they quickly find that these builds are not good and they have to abandon what it was they want to play. The Turrent engineer specifically being really bad is what got my boyfriend to quit the game because that's what he really wanted to play.
Even more issues is the difficulty of some classes in comparison to others that probably should be. Take Elementalist for example. Elementalist should probably have an extremely simple high damage build on their core spec, something that doesn't require too much if any attunment swapping. Yet that isn't viable and the builds that are viable are some of the most knowledge intensive in the game, requiring massive memorization of the class.
The last issue I see is the high number of junk utility skills. There are a lot of utility skills, weapon skills, elite skills that just go unused in PvE. Although some have use in other game modes in some cases they don't get used there either. Engineer I feel is notorious for this as if you're running them there are few utility you really want to take that you couldn't get better utility from elsewhere such as your toolbelt skills on more useful skills or even elite spec skills. Gadgets and turrets have been the target for a lot of these issues as they often struggle to keep up with Kits. Kits too have these issues where in order for the engineer to get the best use from their kits they need to effectively swap out of those kits after using 1 or 2 skills. Which leads to more new player confusion.
I'm not saying every aspect of the professions need to be new player friendly. More I'm saying that what new players are expected to learn and understand in the long run without having viable standard options as well as simpler options has soured the experience of far too many players I've attempted to get into the game.