I think it's even simpler than that, I think it's the feeling of there being cohesion within the kit, and of 'building up to a payoff' (with the payoff being 'everything is now fully DOT'd up')

Without things like being able to spread DOTs (or having DOTs plural, in fact), the cohesion is lost, and the DOTs are just 'damage buttons with a conditional'. It becomes like a self-fulfilling thing, where they get more and more simple/lose interactions, then eventually just get removed 'because they're boring anyway'. If Iron Jaws didn't exist, BRD's DOTs would have nothing going on. People complain that the Song Procs no longer work off of DOTs, because that makes the DOTs have less cohesion with the kit as a whole. They could have changed it from 'when DOTs crit' to '% chance when DOTs tick', but they went one step further, removed the DOTs from the equation entirely, and now the DOTs just kinda.. are there. Wouldn't be surprised if they just combine both of the DOTs on BRD into one so they can remove Iron Jaws and the second DOT as a keybind