TBH, it's better as a DOT as it's A: Thematic to SCH, being known for its DOTs in the past, and B: let's say it deals 500p over 15s (5 ticks of 100), if it were a single 500p hit, it'd be much more swingy due to Crit/DHit variance. As a DOT, not only can it not Direct Hit at all (removing that variable from balance calculations for the devs), but the chance to Crit is split across 5 'attempts', making it more consistent rather than 'all or nothing'. It will snapshot the Chain critrate buff upon application too, so that's not a problem
Now, it being locked behind Chain is a separate 'questionable decision'
To elaborate on this, to make comparison more easy to visualize: In WOW, Medica would be 50p, and would have a 15s CD. Medica 2 would have a 1min CD, and be 100p, plus 20p per tick. Cure 3 would be target capped to 5, heal for 150p and have a 1min CD. The sheer power of Medica/Medica 2 compared to their resource cost, and especially their accessibility (being 'there is no CD') is absolutely obscene, and because they're so powerful, it means OGCDs have ended up being scaled 'based on the baseline provided by Medica/Medica2'. You can see this with AST especially, Celestial Opposition, the level 60 skill, is quite literally 'Aspected Helios, but as an OGCD', the potencies are identical.
We could cut every healing potency in half, and healing would still be way too accessible compared to what most content demands of us. I once joked that a SGE could heal an EX roulette with nothing but Kardia, Soteria and Krasis to buff it. Well, turns out the SGE doesn't even need to be present, since you can just replace them with another DPS. How SE thinks that 'the ability to replace one of the three roles in the 'holy trinity'', in a game built with the holy trinity as a core aspect of the gameplay, is acceptable, is beyond me. It's absurd. At least when it happens in WOW (healers are not required to clear content), they patch the game to make healers required again by the time the next patch comes out. SE has let 'no-healer runs' of everything from EX roulettes, to tanks soloing the normal mode raids, to a no healer clear of the current hardest content in the game, for over 2 years.
And no, I don't want to hear about how 'it took skill to do the no-heal TOP run' or 'it took a lot of luck'. I don't dispute how much skill and luck it took. The fact it was possible at all is an abhorrent glitch in the design of the game. It shouldn't have been possible in the first place, not with any amount of luck or skill.