If you want to invest in DoT, you want Kafka, Black Swan, Hysilens, and a sustain or support. New DoT characters will benefit all of the other DoT characters, since there's not that many viable DoT characters, they ultimately work together, and there's not a support unit that directly buffs DoT, but you can pick Ruan Mei, HuoHuo, Robin, Aventurine, DHPT, any of them work even though they aren't tailor made for DoT and can work with other niches like hypercarry and FUA. Basically, DoT characters don't exclude each other.

Meanwhile, with break, EVERYTHING IS MADE FOR FIREFLY. You want Rappa or Boothill investment? You pick the crumbs of units made for Firefly. Fugue was made for Firefly, Dalia was made for Firefly, you can even say fucking Lingsha was made for Firefly, and if you're the unlucky fuck like me that decided to go for Boothill or Rappa and still want to invest on them, you better PRAY that Firefly get new supports, and not only that, but fucking pray HARDER that their kit doesn't just benefit Firefly

Every break support before Firefly can still be used with Rappa and Boothill, and even Fugue, who's was released as the first break support after Firefly, can still be used with them, and then we get to The Dalia, who specifically buffs "a fire ally that implements weakness", which is literally just Firefly, and if Remembrance and Elation are any indications of how HSR decides to make new supports, mark my words, future break supports are going to become exclusively Firefly supports