They both started very bad. Biden improved greatly and Trump got progressively worse. The most strident doomers are making second- and third-order metacommentary.
TBF, I think "how would someone react to this if they stopped watching after the first 15-20 mins?" is a salient question for a not-insignificant number of viewers (whether it's a significant number of persuadable voters is a different question)
Even the opening where Biden was at his weakest, the moderators straight up said trump’s justices killed roe, and trump said that was good. Not a good debate for trump except that he defied expectations by not ranting about electric sharks and low flow toilets