Edit: So based on the information everyone has given me. I am indeed crazy for thinking of having 3 DPS for this game. I would like to add I'm okay with all the down votes. I understand people may not like my opinion. I guess I was thinking of what I usually go through when I do eternals but not in comms. But hey, that's why I am trying to find a group to interrupts are much easier to coordinate.
I feel it can be difficult to prioritize certain kicks when the tank just has to soak damage. But they can only soak so much until it becomes to much for the tank and healer can handle. Let's just say you're running a high eternal. Tank pulls 5 casters with each pack of enemies. Yes, they have some sort of CD but it only last so long.
IMO if you want to keep it 4. Maybe have a kick or some form of CC for the healer has well. Or shorten the kick timers. Maybe 5 seconds for tank and 10 for DPS. I have played all roles (eternal for DPS, Champion for healer, and just started tanking). It can become overwhelming for all roles because certain mechanics NEED to be kick. What happens if everyones kick is down. Yes, you can argue to manage the kicks better. But you can only do so much depending on the mob packs you pull.
Maybe I'm crazy for thinking this way.