Rollins isn't a terrible tackler - Randall is
As for CB traits - no, tackling is not #1 on my list, coverage ability is; but Randall played predominately at Safety, facing the LOS, and didn't have to demonstrate CB skills.
Coverage ability encompasses a few critical traits that a player either has to have, or he has to find a way to work around that shortcoming.
Backpedal, hips, speed, recovery speed, overall technique (pressing the sideline, etc), playing the ball, anticipation and instincts... I'd put all those traits above tackling - BUT...
I think Randall has a very average backpedal and average hips; he has decent speed, but he looks like a one-gear runner; he shows decent technique when he's in position downfield, but he got into that position from deep safety, not CB; when I did see him take a guy off the LOS, he was slow to react, slow to flip his hips, etc (look at that footage that someone posted of him covering Montgomery - which I can find, lol... )
Throw in those things with his poor tackling, and general lack of physicality - and I don't think he's a 1st rounder.