Lamar is .002 or .003 slower then Zaire Alexander, who ran a 4.38 at the combine. With the amount he has beefed up, he might be as slow as 4.45. His true strength is going from 0 to full speed very quickly and breaking ankles with full speed cuts.
2 things for you:1) Lamar was criticized for staying in the pocket too long- not tucking and running too soon and 2) there is no way he has a weak arm. He has a bad habit not to turn his hips on short throws that leads to poor accuracy and velocity on those throws. A good QB coach will rectify that issue.
You need to watch some film, lol. Lamar is anything but a one read weak armed QB. If anything, he stays in the pocket too long and There is a YouTube video of him throwing a 95 yard pass in high school.