Ben Johnson, I believe, was the one that set the bar for Caleb at 70% when he came to Chicago. Having worked with Goff he saw how much that could overall improve the game. Since Goff joined the Lions here's how he's trended:
Interestingly, Johnson didn't start as the OC with Detroit until 2022 when you notice a dip from 2021-22 then back up again gradually until Johnson left at the end of the 24 season. Goff has always been a pretty decent passer. What kills him is his lack of mobility. He gets REALLY erratic after he's been hit a few times.
I thought it interesting to see Williams had a 62.5% passer completion rate his rookie year (this despite his insane number of sacks). But then with his first year under Johnson dropped to 58%. I suspect he's tracking similar to how Lawrence is and get back to mid, maybe high 60% next year. And maybe in his third year of the system (like Stinger mentioned) we'll see him closer if not surpassing the 70% mark.
NOTE: Drew Brees currently holds the record percentage rate at 74.4 (2018) so its not totally out of reach. A handful of guys have surpassed 70% in the 'modern era' in more than one season so again, nothing says Williams couldn't join them.