Well:
In a game like Destiny, let's call it shield FPS, where your health does not regenerate unless you don't take damage for a period of time and then start slowly getting it back, a DoT is insanely overpowered just by what it is.
Apply a DoT on a player and they need to back out for the duration, otherwise they are safe dead unless it's an engagement where you outnumber the enemy.
In a game like let's say League of Legends you have health regen no matter what happens. When taking damage, you regen. When having a DoT applied, you regen. It's not much, and your health pool is much much larger. There is the difference

In Destiny your health pool is tiny, ~200, and it can get deleted within a fraction of a second at any given moment (for example team shooting) or in about 1 second in a usual 1v1 engagement. You have outplay potential by cutting angles and re-engaging.
A damage over time ability on its own, even if it's 1 damage per tick, is insanely strong and valuable, especially in competitive play. Keeping a player out of the fight for 5 seconds + makes a 3v3 suddenly a 2v3 - easy picking. The weak player has to run, cut angles, wait for the DoT to stop, wait for health regen - then he/she can re-engage or even show themselves in open areas without getting picked immediately by 1 bullet of a HC or scout or even a single pulse burst.

DoTs, unless having a counter like constant health regen or being able to stop the DoT by crouching twice or whatever, has no place in a game like Destiny and is a failure of design because it will dominate the meta.
Try playing 3 Burnlocks in ToO or skirmish, 6 Sunsingers in clash and control are the bane of your existence, especially when they have T5 discipline and a free nade every respawn. Their grenades are currently a mass-zoning and disabling ability that makes outnumbering the enemy as easy as landing a nova bomb.

It is thorn as grenade and it deals 3/4 of your health with one hit as well (given the burn doesn't proc twice or more often cause bugs - same with their melee). Oh yea, the melee that deals 195 damage only due to the DoT that is a 1 hit kill no matter what you do unless you get a kill with red death, charged blink strike (and perk) or void Ramlock melee.