IMO the situation back then was different. Yuan Fang fresh out of the school already got full support of Yuan clan, at that time the strongest among all warlords, while other Geniuses were still building up their force or hadn't followed any lord yet. He simply got a massive head start on everyone and had more cards to play.
The same thing happened when everyone ganging up on Dong Zhuo, or Sun and Liu combining force to fight Cao Cao. It's always about taking down the biggest guy to even out playing field. Now the balance of power has mostly stabilized and everyone is too wary of each other to act rashly, there's no room for that kind of battle royal excitement anymore.
I wasn't talking about powerscaling. It's about the narrative beat of the story. Ravages is an adaptation of RTK, so there are only so many opportunities to create a "final boss" type of character that requires multiple heroes working together to beat. The story frame is set. You can't have Lu Bu behead Cao Cao, or Yuan Shu becoming emperor. That means a "final boss" character needs to fit within the framework.
Yuan Fang worked because Guandu provided the niche for such a character to be dropped into it. However, the next available niche was actually Chi Bi, and Chan Mou failed to slot anyone there, using only the original RTK characters to do the job. I only just realized this because his recent Xun Yu arc is very similar to the original Yuan Fang arc, in that plots within plots within plots were being played out, centered on one character (like the long setup for Yuan Fang in the early chapters), and in the end it all came to nothing (Yuan Fang because Guo Jia cheated, Xun Yu because he couldn't pull the trigger). So Chan Mou seems to be trying to return to tbe narrative beat of the early series. But Xun Yu is not a final boss, and even if he were, he'd have been a weak one. The one being set up to be the new Yuan Fang is the Immortal, but there is no longer a niche where he could become an existential challenge in the story, and not enough heroes to gather up to challenge him. He's basically a localized problem that'll be handled by regular characters. We even know already how he'll be foiled by the Zhao because that's what happened in the original story (and real history). The Zhao being introduced so late and lacking development for readers to be invested in also makes the path the story is taking unconvincing narrative-wise.