Mkopec,
Excellent points and I agree with it. As mentioned in the video Mughal supplied, people are horrible at prognostics. It should be easier for EQN to avoid the pitfalls of GW2 and they are expanding upon the variation a group can have to succeed. I liken it to a Navy Seals team. Yes, they have specialties but they also are extremely versatile as well. A sniper isn't just useful at long distance kills even though he is at his greatest strength when used in those situations. This game will hopefully follow a similar path.
For instance, and this is a long example, there is an orc fort with about 50 occupants who get reinforced, resupplied, etc every week. Normal routine is 10 foraging for food in the nearby forest, two sets of 4 wandering guards(sentries) around the outer edges and two sets of 4 guards at each entrance(2 entrances for solid defense). There are two sets of 3 that are carpenters, blacksmiths, etc and then an inner guard of 5 who wander the fort. The keep has two guards at the entrance and another eight or so within which includes the captain, his two lieutenants, and several bureaucrats. Old EQ would be to leave the foragers for people to camp, camp the wandering guards, camp an instance, etc. If you wanted to kill everything, you would feign pull, or use typical trinity combat. Your only problem was aggro range and usually the game or your mezzer set it up so you could handle small groups like a meat grinder. Effective, but kinda boring in 2015 and on.
What if you could vary tactics based off what you want to do though? Lets say you want to kill the foragers first? Mezzer will take care of the 4 at the wagon while the other 5 assassinate 5 foragers. That leaves one who either runs, tries to attack someone, etc. Then you take care of the remaining 5. Healer not needed this time. You do the same to the wandering sentries. Then, you change up the group for the fort. You med for 5 minutes and then have one mezzer, one healer, a tank and 3 dps. Or two healers, two mezzers a tank and a dps. Depending on what you feel are the best tactics for further encounters. Depending on your group makeup and the classes learned within, you could have 4 rogues at a given point. Four wizards or three tanks and three healers. Would these be optimal setups? Maybe for one type of fight. Maybe when you feel like challenging yourself and want bragging rights.
Four rogues could wipe out the sentries with a mezzer and healer as situational backup. Maybe in the captain's war room, it takes three tanks, two healers and one slow dps to easily win the fight? Or two mezzers a healer, tank and two dps. Maybe you try all of the above at different times or days. You can vary tactics because there isn't just one way to do this. That's what I am hoping for at least. Probably won't get it but I can hope. The multiple class system can allow a group of friends to vary tactics based off just the classes known. You don't have to yell for a mezzer or wait for certain classes to do content. You just have to have the basics for what you want to do. I think healers and tanks will be basic early classes. Later on, variety can be used as people progress their characters. Trinity still can be viable. It just is one option though.