Yeah, that was the knock on Rambo coming out of college. His open field tackling was very suspect which is a huge problem for a FS as he is the last line of defense. He didn't square up and he dropped his head. Johnson made him look like what he is.......a rookie. Good news is its very fixable. Bad news is it takes a while.
As much as people pick on Reed Doughty you can see how good he is and why it is hard to replace him. Thomas got freight trained and Rambo looked like what he is a rookie. Both of the young guys have better physical skills than Doughty, now the question is will they become better football players. As j_y said there is time to find out, but I have been saying for months you can't just hand guys positions, they have to earn them.
Whole defense got torched. Defensive line not holding their position, Rak took a wrong angle and Johnson is going to make most safeties miss one on one 20 yards down field.