How to get people to tank!

[Khalithar]

It's the need for capabilities for manipulation and consequent interaction (enmity, CC, and kiting, in some of their simplest terms), whether they be given to all classes or not. If there's nothing for your play to build around that of others, combat complexity falls drastically.

I actually wanted to add more to this specific part of the post as it was something that really stood out to me in the early days of doing dungeons in GW2. Due to the lack of trinity based systems and your survival/healing largely depending on your own abilities and ability to avoid things I rarely felt like I was actually in a party of players doing the group content or even the open world FATE-style content. Unless I made a mistake and needed to be revived, the other players could have been NPC's for all I cared since a lot of came down to being self sufficient. I could best describe it with the phrase that GW2's role-less system was like "we're all playing alone, together." Due to the fact that I couldn't really do anything to buff or support my party (this way back in the days where you wanted to max out your damage as much as possible, not sure if the meta still favors that) outside of reviving them, I never felt like it was part of a cohesive group.

Compare and contrast to a game like this one with the trinity and what do we have? The ability to debuff an enemy so it deals less damage to the party or the party deals more damage to it, using abilities to protect and support each other, aoeing down mobs while the tank holds them in place... it "feels" much more like an actual team effort in my opinion. I agree with you that it IS stale and convention-driven, but alas that's part of the issue, sometimes popular things are popular for a reason, because they work.

[Shurrikhan]

I actually wanted to add more to this specific part of the post as it was something that really stood out to me in the early days of doing dungeons in GW2. Due to the lack of trinity based systems and your survival/healing largely depending on your own abilities and ability to avoid things I rarely felt like I was actually in a party of players doing the group content or even the open world FATE-style content. Unless I made a mistake and needed to be revived, the other players could have been NPC's for all I cared since a lot of came down to being self sufficient. I could best describe it with the phrase that GW2's role-less system was like "we're all playing alone, together."

Alternatively, you could take undermanned, undergeared content in B&S, where if each player isn't timing his rotations in order to CC-fill, you're all screwed. Both it and GW2 are without any real "healers" (SMN has it tacked onto a couple AoEs in B&S, just as a ranger can take a 180* into Druid on GW2) and the capabilities aren't at all divided by roles (apart from KFM/BM bonus threat skill specs), but because that one has more that can be done, people don't take dodge-spamming and necessary damage taken as "self-sufficiency". Because damage can and should be hard-countered, but no one player can hard-counter everything (except a KFM/BM against a single mob, which to me is still regrettable), none are "self-sufficient".

It's a difference in having things that can be done, and therefore temporary "roles" to be fulfilled or responsibilities to be split. GW2 is simply shallower still, in most cases, than even XIV, because there are fewer tools or meaningful manipulations available. At best, in place of enmity modifiers and taunts it gives back decent kiting. But that's not because XIV is "trinity" and GW2 is "role-less". It's because they're both "low-tool" and therefore "low-interaction". You do not need passively or rigidly set roles in order to achieve division of responsibility; in fact, doing so only limits, outside of player choice, the means of interaction available to the party. I'm not saying specialization should never occur, but as a convention its best use is in long-term parties in games that allow for actual customization—as an MMO convention it streamlines content, sometimes seemingly for the better but usually ultimately for the worse.