This is immensely reductive.
Why do people assume that when someone says "X can be done without Y", that they're looking for Y? I have played GW2. What I suggested, is nothing like GW2. I have also played several other MMOs that had no permanent tanks, but in no case has that necessarily meant "no well defined roles". It meant only that responsibility was not left to a small portion of the party, unless the MMO failed (as with GW2) to give their players a means of conducting those roles.
The "spammy mess" you speak of in GW2 is a lack of "role" toolkit among those alleged "non-roles", making it impossible to fill those functions for which (a portion of) Trinity roles would be responsible. But that does not mean that you suddenly need specialists for the role, or that there should only ever be two levels of role capacity (the role, and the non-role). You can have multiple shades and styles of capability, so long as you embed reasons for which they cannot take that role with permanent uptime.
Imagine if tanks had no bonus enmity for instance—that is the source of your "spammy mess" in GW2. But the issue isn't not having "tanks". The issue is not having enmity skills. The difference in design, should such toolkits actually exist, is that anyone could participate in tanking, not just taking threat and then dying, and would be responsible for managing that responsibility (saving the current target) with their personal survival and output, in light of incoming raid damage and outgoing raid healing, etc. So you could have a Monk splitting damage during whatever period he is able least affected by positional bonuses, a Dragoon just before Life Surge, etc., along with alternate utilities such as a Bard drawing off enemies slowed by a Miasma II for a brief kite and position them for a Freeze or Tri-bind (because, gasp, we allowed those skills to work again). That ends up highly timeable, sync-able, by-event, quite the opposite of a "spammy mess" (in my opinion, a term better fit to the meat-shielding and tunnel-visioned DPS or mass pulls of 'unadulterated' Holy Trinity play).
So any solution presented to (more fully) mitigate DPS queue times outside of your "only real way" is thread derailment? Really? In that case, what's to talk about? Should I just say "you idea would help, but would be ultimately insufficient" and end flatly, since a counter-suggestion would be taboo?