On linebacker "shortness":
This is all about "extension", not height. Because of the changing nature of the offensive game {spread field and stress everyone in the back 7 or 8}, even ILBs must have some "extension" to defend the pass, especially vs TEs. So, when you hear the height of some prospect, mentally say: how long are his arms? [I've said ego-centrically before that my own height is "just" 6'0", but the wingspan translates to 6'3". If I'd had any talent, I would have probably passed the measurables criteria.]
That said: if an ILB prospect has SPEEEEDDD and great reaction instincts, that cures almost all other problems in the end. If I was recruiting ILBs [or DBs], and could actually assess the following, I'd rate
a]. instincts;
b]. speed;
c]. extension; .... in that order {power sufficient for the position would be of course a starting point}. {and brains}. {and character}.