The way Star Rail design process works is that you have characters/teams centered around a particular mechanic. There's usually 1-2 DPS, 1-2 supports, 1-2 sustains forming the core of the mechanic. And the characters are spread out and sold over time until you build up that best in slot team (that is, assuming you're a hardcore gamer pursuing the meta).

Then the weekly/monthly "dungeons" are balanced around the current banner character and/or the current mechanic.

So yeah, pure numbers wise, old DPS like DHIL and Jingliu can do as much damage as current DPS on paper. But the current endgame doesn't cater to their strengths and mechanics, so they don't perform as easily as the current "meta" teams. Hence people who pursue the current best "meta" are always going to be pulling for the latest "core" DPS/support/sustains. When the next mechanic rolls around (probably with 3.0 patch), people who pursue the meta will shell out for those characters.

> Since you said non-acheron DPS get the same out of Jiaoqiu as a healer, then what would be the appeal of pulling him?

For the people who don't care about the meta, they're usually pulling by the looks or the lore or the character design, so they don't really pertain to this discussion at all.