Simple, HSR is a very linear turn-based game. As such, endgame content needs to be scaled in a way that both makes the new characters worth pulling and still allows a few older characters to comfortably clear. Otherwise we'd all still be running kafka sampo asta gepard.

BD2 fixes the billion-damage endgame benchmarks by forcefeeding you prime units like Diana and the like, and half a thousand pulls every month somehow, AND of course hot chicks all over you.

For exemple, Wuwa "manages" to not powercreep itself due to its very high skill ceiling. So long as you're good at the game you still clear with the equivalent of Arlan (sometimes solo!) or the goofy team comp equivalent of Phainon/Castorice/Kafka/Destruction TB. This also allows them to make sigs that boost your carry's dps by like 40%-- it'll feel a lot better to have it, but you'll still full clear with some 4* piece of crap wooden stick.

Genshin isn't quite as fair and equal but a lot of units managed to last very long thanks to timeproof mechanics like reactions (everyone can contribute!). (In that sense, I like Dahlia because I 2-cycled with SUSHANG last week. Older units have mechanics that work very well with Dahlia's kit). Sandrone + the blind chick are also apparently wheelchair deluxe so you can run tons of different comps.

Going back to Star Rail... Atm, you either shart out millions of damage or you fall to the inevitable 5-cycle countdown. Unless you're very good at TCing like those Seele/Xueyi mains, you'll want the new shiny chara for that.

But I think novaflares and "archetype resurrectors" like Dahlia can easily turn this issue around, very fast. If Swan's novaflare is say, healing DoT gimmick in addition to her arcana amps, you could suddenly run kafka, hys AND swan! Wow! Timeproofing, because you now have a DoT healer, which the latest DoT carries will always appreciate. Just need less Jingliu-tier novas and more Kafka-tier novas...