Obviously yes he was better prepared than Spencer was. However, I can make the case that Penix had more pressure in his first start than Spencer. No one on the planet expected Spencer to go out and win.
Even Rattler himself pointed out that going from #3 to #1 in such short notice was a “shell shock”. Add that to being behind a depleted OL and losing your #1 WR after 4 or 5 plays and I’d say Rattler was put in far worse position than Penix was in his first start.