All roles are as engaging or as boring as you make it.
DPSing can be mind numbing at low M+. But, at high M+, it can get quite stressful as you try to maximize damage while dodging mechanics, interrupting / stunning, etc.
Tanking can be boring if you always just go the same route and do nothing else. Or very involving if you are constantly watching your group and mobs, controlling the pulls, interrupting, timing the defensives, etc.