Yeah, it definitely doesn't tell the whole story.
Trent was first injured in the Browns game and played on a bum ankle. Purdy did not play well in that game so that could be counted against him too.
Purdy - 87.9 https://www.statmuse.com/nfl/ask/brock-purdy-stats-without-trent-williams
Hurts - 78.4 https://www.statmuse.com/nfl/ask/jalen-hurts-stats-without-lane-johnson#
Yeah, it definitely doesn't tell the whole story.
Trent was first injured in the Browns game and played on a bum ankle. Purdy did not play well in that game so that could be counted against him too.