Wu Li, although capable of delivering punches weighing four times his own body weight, could only do so after properly adjusting his stance, an opportunity that clearly wasn't available in the ring. Even a delay of 0.5 seconds in a punch could mean missing the opponent entirely, let alone taking a few seconds to adjust one's posture—it was almost like becoming a punching bag for others.
Unless there was a significant disparity in strength between the two fighters, then perhaps such heavy punches could be viable. However, when the skill levels were too mismatched, the use of heavy punches didn't really matter anymore—any type of strike would suffice.