Lance Stroll's first season in 2017 included a podium. He scored 9 more points in that race than his entire 2018 campaign. If that doesn't tell you what Williams were dealing with in 2018, nothing will. Even with a Mercedes engine at their disposal, the car was so slow through the corners that it rarely mattered.
The poor standard of the FW41 makes it difficult to accurately judge Lance Stroll's season. His weakness remains his qualifying as rookie teammate Sirotkin held a narrow advantage throughout, something he needs to improve on when he joins his father at Force India/Racing Point/Team Name Pending in 2019.
His performance at Monza deserves plaudits, as does his ability to make up places on the opening lap of Grands Prix, but it's almost inevitable that 2019 will be an improvement for the youngster.