There just wasn't any way to beat branching experts head-on as long as they had access to techniques suitable to their stage. Liam could match that arsenal, but his attacks would always be weaker.
On top of that, Liam had his Qi reserves to take into account. While immense compared to the average rooting expert, rank 3 techniques would still empty his body and core in no time. The Qi-Storage Pill could compensate for that weakness, but they were no permanent solution.
With branching experts always moving faster than Liam, he wasn't at liberty to eat pills whenever he wanted. That would create a window his superior opponents could exploit.
Lastly, there was an issue of poor match-up. Jessica's core dealt with air, while most of Liam's poison relied on smoke. He just wouldn't be able to infect her with his usual tools.
